On macOS, simply rename .imazingapp to .zip and unzip. Then, do your thing, and re-zip the contents of the unzipped folder, not the root!
Step by step:
MyApp.imazingapp -> rename to MyApp.zip
Unzip MyApp.zip -> you'll get a folder named MyApp
Edit files in MyApp/Container/. Don't delete or add files, only edits are permitted!
Re-zip the CONTENTS of MyApp, not the MyApp folder itself
Rename to .imazingapp
Restore with iMazing
Again, it is not possible to add or remove files from .imazingapp. For that kind of advanced work, you need to use iMazing to make an editable backup, edit app files in the backup (extract file->edit->re-inject, or delete files, or add files) and then extract the .imazingapp from the editable backup. You can make editable backups with the free trial, but file system operations are limited to 100 transfers.
Enjoy!