Why the bollocks would you even try?
Because I already own the tyres!
It's £300/year or thereabouts to swap winter and summer tyres. Spare wheels for both cars would cost £450 or so and then I'd need the tyres fitted to those for £150, which is a big outlay.
It'd be nice to be able to do it myself, and for that price I could buy whatever kit I need.
There are wheel balancing rigs available. I think you just have to mount the wheel on something free spinning and horizontal, so that the heaviest part sinks to the bottom.
you need a special very expensive reaming tool that only proper wheel changing places have
You do? Whenever I've had it done the guy has a rig that tells him where the heavy spot is, and he just sticks weights to the rim. Never seen any reaming.