You can do that although you need a new fzp file with a unique moduleId, but I think it is better to separate all the svg files (giving them new file names even if they are identical) to avoid making a change in one part that then affects another part that you may not have expected to change. I don’t think there is any standard answer, there are some parts in core that share svg files (we are working on making such a change to 6 or 6 pot parts in core all sharing a common schematic svg.) In that case it is unlikely there will be a change that conflicts but I would rather see the files all be unique. Selection of multiple variants in Inspector is done via a common family name and one (or more) properties that are different that will then appear in the inspector window and change parts when selected. In theory I think the parts are supposed to all have identical pins so they will swap correctly if connected in a sketch, but there is a case to be made that it is better to be able to select from a list of parts in a family before wiring (where the parts may have a different number of pins.) There isn’t currently any standard and at least in my view we probably should have one (along with more standards for parts), but right now bug fixing is (and should be!) taking priority. That discussion is taking place (slowly!) in this forum post
Peter