Customising info.plist file for an AppleScript applet - applescript

Question

So basically I have this application made from AppleScript. Now I'd like to customise some information (e.g. bundle identifier, version number, etc.) However, it seems as if even the slightest changes to the info.plist will cause the script to… not work.
Any idea how to change the info.plist of the AppleScript application without breaking it?

Answer 1

There are only three requirements for editing a plist file:
Don't change anything on the first four lines. They should always look like:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
Don't use anything except plain-text characters (no curly quotes, rich text, strange characters, etc). I recommend using the free version of BBEdit, which will keep things nice.
Don't break the hierarchical key-value structure. Plist entries have the form:
<key>KeyWord</key>
<value-type>whatever data</value-type>
where the value-type can be 'string', 'real', 'integer', 'date', 'data', 'array', 'dict', of one of the booleans 'true' or 'false'. It's standard XML style, with opening and closing tags (distinguished by a slash) and singleton tags for true and false (where the slash is at the end of the word rather than the beginning). Dictionaries can have key-value pairs within them, arrays have lists of values without keys, you can nest as deeply as you like, but you must always open and close tags in the proper order.
Common errors are:
accidentally deleting an opening or closing angle-bracket
overlapping opening and closing tags for nested elements (e.g., open tag for a dict, open tag for an array, close tag for the dict, close tag for the array)
separating keys from their values (value elements must come immediately after key elements

Answer 2

An additional concern in modern days is that applets are now codesigned by default. This means if you modify any part of the applet (including Info.plist) outside of Script Editor, after creating it, it will now have an invalid code-signature.
For some purposes, that won't matter, or be noticeable — but, especially if you control "System Events" or use accessibility features, you'll get obscure, confusing failures until you fix this.
Luckily, it's easy enough to re-sign the application-bundle after you've modified the Info.plist — simply run the following in the Terminal:
codesign -fs - --preserve-metadata=entitlements /Applications/YourApplet.app
The -f overwrites the existing (now incorrect) code-signature; the -s - allows it to be an ad-hoc signature (same as what was already present); and the --preserve-metadata=entitlements is the important part that maintains the Script Editor configuration of your script's permissions.