This thread:
is an excellent way to edit the default menus by overriding the Default pacakge. But that’s not what I’m after.
I’d like to create a plugin that can, for example, go into the Help menu and remove the “About Sublime Text” entry.
Is this possible?
No, that’s not possible unless your plugin was to do the work of creating the override for you instead of your doing it manually.
Resource modifications are additive by design and not subtractive; presumably that’s because any package can do whatever it wants with resources and so conflicts might arise; that’s just a guess on my part, though.
For example if my package wants to add items to the help menu after the About entry but your package loaded first and removed it, something somewhere is not going to go well and it’s going to be a maintenance nightmare to sort out after the fact.