I would try DeRez.
Steps:
1. Install MPW. (I put mine on the Applications folder;)
2. Open the MPW Shell;
3. Delete everything and type this:
DeRez -1 "Macintosh:Applications:MPW-GM:Interfaces & Libraries:Interfaces:RIncludes:" "Macintosh:Desktop Folder:MyApp" Carbon.r -s CODE -s DATA -s RELA > "Macintosh:Desktop Folder:MyApp.txt"
Make sure it's a single line, then position the cursor at the end and hit ⌘+Return.
Now, you can see a file will be created on your desktop. It's a text file with a creator type set to MPW. You can modify that with the FileType app or even MPW itself, or just drag into SimpleText.
Notice how we're skipping the resource types for "CODE", "DATA" and "RELA". They export a bunch of encoded stuff you probably don't care about. If you do, just don't exclude it. Removing the stuff after, and including the ">" sign will output the stuff to the shell.
You can put the new resource code into a file with the ".r" extension. If you use an IDE like CodeWarrior, there should be an option to run server tools there, and you can use it to re-encode this into an .rsrc file to be used by your project. Then you can manually change stuff on ResEdit.
Is the ".rsrc" file just the file created in ResEdit with the resources needed by the program? And shouldn't it be added to the project file?
Yes, the ".rsrc" is a file made by ResEdit. When programming with the help of resources, we make a file like that and set a bunch of data we replicate in the code. Stuff like window IDs. You can add a bunch of windows and id them with numbers like 128, 129, 130, etc, then declare those numbers as constants in your code. When your compiler links all the files, it picks up the ".rsrc" file and merges into the final executable.
But using graphical interface apps like ResEdit is not very good for versioning code, so Apple invented this C-like syntax to describe the resources instead. We use these tools Rez and DeRez to transform the stuff from code to ".rsrc" and back again. Rez compiles the code into ".rsrc" and DeRez decompiles it.
MPW is the toolset that Apple provided for developers that contains these tools. They can be used by other IDEs via a thing called a Tool Server. On CodeWarrior, for example, you need to link a folder from MPW inside CodeWarrior's folder, so it can find these tools. Then, in your project, you drop the ".r" file with the resource code, and spin up the server. Then you can select Rez and it shows you a GUI with options, so you don't have to poke about with a shell like we did on MPW in my above example. It then creates the ".rsrc" for you by encoding it with Rez.
The step-by-step I provided above is for using MPW to manually extract the resources code that would be in an ".r" file. It's an easy way of copying the resources from any file.