I would find that confusing, as an observer. On at least one occasion I inadvertently added an unrelated photo to an OBS, and it was pointed out to me in a comment by an IDer - something along the lines of “the organism in photo 3 is different from the organism in photos 1 and 2. You should make a separate observation,” which made my error clear to me. As a newbie, I wouldn’t have understood if informed that I needed to “split” or “duplicate” the OBS.
I think you should be careful about making things more confusing to newbies, who I suspect are most likely to make the kind of OBS that needs splitting. There can be a steep learning curve for using iNat, both as an observer and as an IDer.