How to change button sets for existing mods without all custom content in the mod getting removed? (for some reason, only part of the title is showing)

So one problem with Visions of the future series, especially VotF 4, is the missing button sets for a lot of custom units. This is due to the campaigns being made before Firegraft existed.

Now I've realized that Firegraft is the application that can add button sets and it looks like a very easy thing to do, the problem is that I cannot for the life of me figure out how to edit the button sets of an existing mod without everything else in the mod disappearing. Opening a mod opens it but if I try to save it, only the custom button sets are kept, everything else in the mod before I opened it such as custom graphics and such ends up being gone. Can anyone help me out here? The change I want to do is so simple and easy too, I just want to change the button set of [6] tank turret (tank mode) from none to Basic commands and add an attack button to the button sets for defilers + heroes.

When it asks you to replace all contents of the mod with external archive, which actually says in all caps that it will clear out current mod, don't press "Ok".

oh so that's what they mean by archive.... Thanks!