Unless all the old sealer is completly removed stain is just never going to soak into the wood. You would be applying a new sealer over a liquid that is just floating on the surface so both the new stain and sealer will just wear off fast.
It's one thing to do some touch ups if the sealer and stain have worn through in high traffic areas because there's bare wood for the stain to soak into. The stain will soak in where the wood is and just wipe off the sealed areas. But to change to a differant color it's has to be stripped.