Back in the day, I disassembled many freewheels, including taking cogs off the freewheel body. There were no standards. Cogs from one freewheel maker were not going to fit on any other freewheel. The thought that you might be able to create a 10 speed spaced 7 speed freewheel is silly. The freewheel body has steps between the largest and smallest cogs. Reducing the thickness of the spacers will create gaps when the diameter of the freewheel body changes. Freewheels are fundamentally different than cassette freehubs.