The only reason why you wouldn't be able to edit inserters is if the other mod changed them to be uneditable.
This mod has a thing in it that changes all existing inserters to be editable. Other mods then have to change their own inserters to not be editable (Either by adding them to the block list in my mod, or editing them to turn on the base game's uneditable tag, after I turn it off)
So, if you can't edit the inserters from another mod, it's probably because they intentionally did it.
