Well in the Super Mods the function for model switching does not just switch the model, but actually sets many of the player's attributes to match the ped and I cannot to much about some of the things it changes, so you're not just switching your model, but basically becoming the ped because everything about the player changes. Since you basically are the ped now, if the ped's unique model status is just 1 (or 01 00 00 00 in hex/ide.img) then there can only be 1 copy of that ped spawned at once, and you'd be that ped.
If you go into one of the adult peds that can have multiple copies, then maybe you should see peds of the same type still spawning.
In Super Mod 5 there should be options to change ped's unique model status (spawning).