1. Ctrl+click the droplet > Show package contents
2. Open Contents/Info.plist
3. Look for "dplt" and imagine your own "CFBundleSignature" (formerly called
"creator code"). Typically, something with all caps, such as "UYTR".
Substitute "dplt" with "UYTR".
4. Add a new entry to the "plist" file, similar to "CFBundleSignature", but
called "CFBundleIdentifier":
-Key: CFBundleIdentifier
-String: com.mca-plus.mydroplet (for example)
4. Save and close.
5. Now go to the Finder, compress the droplet and delete it. Empty trash.
6. Uncompress and now you're ready to go!
When you edit the plist file (changing the "CFBundleSignature" and adding a
"CFBundleIdentifier"), you are giving a unique identifier to your app, so
LaunchServices can recognize your app between lots of other droplets and
apps.
And when you compress-delete-uncompress, you are forcing LaunchServices to
read the plist file of the "new incoming app in the system" and add it to
its database of "identifiable apps". Now you can force whatever file you
wish to be opened with your droplet.
Cheers and good luck!
jj