diff --git a/Blueprints b/Blueprints
index 090813e..fa85eda 100644
--- a/Blueprints
+++ b/Blueprints
@@ -19,7 +19,8 @@ bootstrap_go_package {
 bootstrap_go_package {
     name:    "blueprint-parser",
     pkgPath: "blueprint/parser",
-    srcs:    ["blueprint/parser/parser.go",
+    srcs:    ["blueprint/parser/modify.go",
+              "blueprint/parser/parser.go",
               "blueprint/parser/printer.go",
               "blueprint/parser/sort.go"],
 }
@@ -67,3 +68,9 @@ bootstrap_go_binary {
     deps: ["blueprint-parser"],
     srcs: ["blueprint/bpfmt/bpfmt.go"],
 }
+
+bootstrap_go_binary {
+    name: "bpmodify",
+    deps: ["blueprint-parser"],
+    srcs: ["blueprint/bpmodify/bpmodify.go"],
+}
diff --git a/blueprint/bpmodify/bpmodify.go b/blueprint/bpmodify/bpmodify.go
new file mode 100644
index 0000000..e17188f
--- /dev/null
+++ b/blueprint/bpmodify/bpmodify.go
@@ -0,0 +1,305 @@
+// Mostly copied from Go's src/cmd/gofmt:
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"blueprint/parser"
+	"bytes"
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"unicode"
+)
+
+var (
+	// main operation modes
+	list            = flag.Bool("l", false, "list files that would be modified by bpmodify")
+	write           = flag.Bool("w", false, "write result to (source) file instead of stdout")
+	doDiff          = flag.Bool("d", false, "display diffs instead of rewriting files")
+	sortLists       = flag.Bool("s", false, "sort touched lists, even if they were unsorted")
+	parameter       = flag.String("parameter", "deps", "name of parameter to modify on each module")
+	targetedModules = new(identSet)
+	addIdents       = new(identSet)
+	removeIdents    = new(identSet)
+)
+
+func init() {
+	flag.Var(targetedModules, "m", "comma or whitespace separated list of modules on which to operate")
+	flag.Var(addIdents, "a", "comma or whitespace separated list of identifiers to add")
+	flag.Var(removeIdents, "r", "comma or whitespace separated list of identifiers to remove")
+}
+
+var (
+	exitCode = 0
+)
+
+func report(err error) {
+	fmt.Fprintln(os.Stderr, err)
+	exitCode = 2
+}
+
+func usage() {
+	fmt.Fprintf(os.Stderr, "usage: bpmodify [flags] [path ...]\n")
+	flag.PrintDefaults()
+	os.Exit(2)
+}
+
+// If in == nil, the source is the contents of the file with the given filename.
+func processFile(filename string, in io.Reader, out io.Writer) error {
+	if in == nil {
+		f, err := os.Open(filename)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+		in = f
+	}
+
+	src, err := ioutil.ReadAll(in)
+	if err != nil {
+		return err
+	}
+
+	r := bytes.NewBuffer(src)
+
+	file, errs := parser.Parse(filename, r, parser.NewScope(nil))
+	if len(errs) > 0 {
+		for _, err := range errs {
+			fmt.Fprintln(os.Stderr, err)
+		}
+		return fmt.Errorf("%d parsing errors", len(errs))
+	}
+
+	modified, errs := findModules(file)
+	if len(errs) > 0 {
+		for _, err := range errs {
+			fmt.Fprintln(os.Stderr, err)
+		}
+		fmt.Fprintln(os.Stderr, "continuing...")
+	}
+
+	if modified {
+		res, err := parser.Print(file)
+		if err != nil {
+			return err
+		}
+
+		if *list {
+			fmt.Fprintln(out, filename)
+		}
+		if *write {
+			err = ioutil.WriteFile(filename, res, 0644)
+			if err != nil {
+				return err
+			}
+		}
+		if *doDiff {
+			data, err := diff(src, res)
+			if err != nil {
+				return fmt.Errorf("computing diff: %s", err)
+			}
+			fmt.Printf("diff %s bpfmt/%s\n", filename, filename)
+			out.Write(data)
+		}
+
+		if !*list && !*write && !*doDiff {
+			_, err = out.Write(res)
+		}
+	}
+
+	return err
+}
+
+func findModules(file *parser.File) (modified bool, errs []error) {
+
+	for _, def := range file.Defs {
+		if module, ok := def.(*parser.Module); ok {
+			for _, prop := range module.Properties {
+				if prop.Name.Name == "name" && prop.Value.Type == parser.String {
+					if targetedModule(prop.Value.StringValue) {
+						m, newErrs := processModule(module, prop.Name.Name, file)
+						errs = append(errs, newErrs...)
+						modified = modified || m
+					}
+				}
+			}
+		}
+	}
+
+	return modified, errs
+}
+
+func processModule(module *parser.Module, moduleName string,
+	file *parser.File) (modified bool, errs []error) {
+
+	for _, prop := range module.Properties {
+		if prop.Name.Name == *parameter {
+			modified, errs = processParameter(&prop.Value, *parameter, moduleName, file)
+			return
+		}
+	}
+
+	return false, nil
+}
+
+func processParameter(value *parser.Value, paramName, moduleName string,
+	file *parser.File) (modified bool, errs []error) {
+	if value.Type != parser.List {
+		return false, []error{fmt.Errorf("expected parameter %s in module %s to be list, found %s",
+			paramName, moduleName, value.Type.String())}
+	}
+
+	if value.Variable != "" {
+		return false, []error{fmt.Errorf("parameter %s in module %s is a variable, unsupported",
+			paramName, moduleName)}
+	}
+
+	if value.Expression != nil {
+		return false, []error{fmt.Errorf("parameter %s in module %s is an expression, unsupported",
+			paramName, moduleName)}
+	}
+
+	wasSorted := parser.ListIsSorted(*value)
+
+	for _, a := range addIdents.idents {
+		m := parser.AddStringToList(value, a)
+		modified = modified || m
+	}
+
+	for _, r := range removeIdents.idents {
+		m := parser.RemoveStringFromList(value, r)
+		modified = modified || m
+	}
+
+	if (wasSorted || *sortLists) && modified {
+		parser.SortList(file, *value)
+	}
+
+	return modified, nil
+}
+
+func targetedModule(name string) bool {
+	if targetedModules.all {
+		return true
+	}
+	for _, m := range targetedModules.idents {
+		if m == name {
+			return true
+		}
+	}
+
+	return false
+}
+
+func visitFile(path string, f os.FileInfo, err error) error {
+	if err == nil && f.Name() == "Blueprints" {
+		err = processFile(path, nil, os.Stdout)
+	}
+	if err != nil {
+		report(err)
+	}
+	return nil
+}
+
+func walkDir(path string) {
+	filepath.Walk(path, visitFile)
+}
+
+func main() {
+	flag.Parse()
+
+	if flag.NArg() == 0 {
+		if *write {
+			fmt.Fprintln(os.Stderr, "error: cannot use -w with standard input")
+			exitCode = 2
+			return
+		}
+		if err := processFile("<standard input>", os.Stdin, os.Stdout); err != nil {
+			report(err)
+		}
+		return
+	}
+
+	if len(targetedModules.idents) == 0 {
+		report(fmt.Errorf("-m parameter is required"))
+		return
+	}
+
+	if len(addIdents.idents) == 0 && len(removeIdents.idents) == 0 {
+		report(fmt.Errorf("-a or -r parameter is required"))
+		return
+	}
+
+	for i := 0; i < flag.NArg(); i++ {
+		path := flag.Arg(i)
+		switch dir, err := os.Stat(path); {
+		case err != nil:
+			report(err)
+		case dir.IsDir():
+			walkDir(path)
+		default:
+			if err := processFile(path, nil, os.Stdout); err != nil {
+				report(err)
+			}
+		}
+	}
+}
+
+func diff(b1, b2 []byte) (data []byte, err error) {
+	f1, err := ioutil.TempFile("", "bpfmt")
+	if err != nil {
+		return
+	}
+	defer os.Remove(f1.Name())
+	defer f1.Close()
+
+	f2, err := ioutil.TempFile("", "bpfmt")
+	if err != nil {
+		return
+	}
+	defer os.Remove(f2.Name())
+	defer f2.Close()
+
+	f1.Write(b1)
+	f2.Write(b2)
+
+	data, err = exec.Command("diff", "-uw", f1.Name(), f2.Name()).CombinedOutput()
+	if len(data) > 0 {
+		// diff exits with a non-zero status when the files don't match.
+		// Ignore that failure as long as we get output.
+		err = nil
+	}
+	return
+
+}
+
+type identSet struct {
+	idents []string
+	all    bool
+}
+
+func (m *identSet) String() string {
+	return strings.Join(m.idents, ",")
+}
+
+func (m *identSet) Set(s string) error {
+	m.idents = strings.FieldsFunc(s, func(c rune) bool {
+		return unicode.IsSpace(c) || c == ','
+	})
+	if len(m.idents) == 1 && m.idents[0] == "*" {
+		m.all = true
+	}
+	return nil
+}
+
+func (m *identSet) Get() interface{} {
+	return m.idents
+}
diff --git a/blueprint/parser/modify.go b/blueprint/parser/modify.go
new file mode 100644
index 0000000..68d8925
--- /dev/null
+++ b/blueprint/parser/modify.go
@@ -0,0 +1,47 @@
+package parser
+
+func AddStringToList(value *Value, s string) (modified bool) {
+	if value.Type != List {
+		panic("expected list value, got " + value.Type.String())
+	}
+
+	for _, v := range value.ListValue {
+		if v.Type != String {
+			panic("expected string in list, got " + value.Type.String())
+		}
+
+		if v.StringValue == s {
+			// string already exists
+			return false
+		}
+
+	}
+
+	value.ListValue = append(value.ListValue, Value{
+		Type:        String,
+		Pos:         value.EndPos,
+		StringValue: s,
+	})
+
+	return true
+}
+
+func RemoveStringFromList(value *Value, s string) (modified bool) {
+	if value.Type != List {
+		panic("expected list value, got " + value.Type.String())
+	}
+
+	for i, v := range value.ListValue {
+		if v.Type != String {
+			panic("expected string in list, got " + value.Type.String())
+		}
+
+		if v.StringValue == s {
+			value.ListValue = append(value.ListValue[:i], value.ListValue[i+1:]...)
+			return true
+		}
+
+	}
+
+	return false
+}