What, if any, wheels will interchange between brands? I haven't tried to pop any wheels off yet but I was wondering if the GMP wheel sets they sell would work without much modification on say a Ertl or Yatming model.

I have done some 1/18 wheel swaps . Ertl is pretty much by itself in its design . I did put some Ertl wheels on a Welly car pretty easy . The one Maisto I worked on had its wheels screwed on . Some GMP's do too . Some of Ertls high end cars have their wheels screwed on too . Basically its trial & error . Most Ertl wheels are snapped on , but there are many different axle diameters . So even among Ertl cars interchangeability is limited . I did buy some GMP magnum 500s that I did make fit on several Ertl cars .. Hwy 61 cars have their wheels snapped on too .