Do you actually ride on the road?
To be fair, using a separate wheel could lead to more issues than using a different tyre.
You really need to change the chain as well. If you don't use a separate chain you are going to wear out chains and sprockets fast.
If you're not doing big mileage then i wouldn't worry about tyre wear, assuming you dont have very expensive tyres of course.
FWIW, just ride your bike (in and outdoors) and worry about spare tyres / wheels / bikes for another day.