Can you mix sizes of indoor and outdoor air conditioner units like a 4 ton compressor and a 3 ton condenser?

Absolutely NOT ! you will end up with more problems,and spend more redoing it because it doesn't work together.And besides a 4 ton compressor needs a 4 ton condensor.3 ton condensor will not have the surface area to cool the freon from a hot vapor to a cool liquid,that is needed for optimal performance in air handler,which is also rated for a 4 ton ,due to the coil size and the expansion valve size.