That's about the size of it .. sort of.
If the aircraft doesn't have any growth capability, or such is not investigated, one can look at the notional maximum strength of the wing in terms of gross weight x limit load factor and then divide that by the revised, higher gross to figure a reduced limit load.
However, it doesn't work the other way for mods. If the gross weight is reduced, one can't increase the limit load .. as all the bits and pieces of things which are bolted or sticky taped to the airframe will have been designed to the original spec requirements.
If one increases the limit load, the wing might be OK but lumpy bits might fall off when you pull the higher limit load.