Hey @jake0 welcome to the forums!
You shouldn’t need to modify the app to enable this.
Basically you need to set the context_change_allowed on the item, and then the context picker will show up.
However you also need to watch out for these two lines:
If you are running the default maya publish accept, then this will disable context change again if a publish template is set, so you may need to implement your own accept method if you were inheriting from the base Maya one.