niko ped is divided in parts(head, hands,bodies;all clothes,feet...)
and noose swat isnt divided, it is all in one model
you have to learn more the skel properties the ped models have to learn how it works.and after that, divide all the model in parts and make it match to the niko ped.
but there is some easier way to play as a swat ped, using native trainer with Model Spawning.
niko model replacing is a real serious issue cuz you will have a mess up in the cutscenes.