Seat does not swap - dunno on the tires
Alas the ex500riders.com forum is down, or I'd point you there for tire recommendations. I know at least one rider there is a big fan of the Pilot Activ, so you might see what you can find about those tires in other places.
The seats have different part numbers between the 93- and 94+ EX's. That usually means they don't swap. FYI, the way I answer questions like that is to go to ronayers.com and look through their "OEM Parts" section which has a copy of Kawi's online parts diagrams. You can go to the EX500 page and it contains links for each year bike, so you can easily compare them side-by-side in two browser tabs or windows. That's harder to do on the Kawi website. They're also known to have decent prices for OEM parts.
<edit>
Oh, one comment on the tires and ride height. Personally, I wouldn't depend on tires for a significant component of the lowering of the bike. It's hard enough to find tires for this bike that you may find yourself choosing between your desired performance characteristics and your desired size. For instance, the Activ's don't come in 130/60, only 130/70. I'd figure out how to lower the bike to the right height so that you can ignore the differences in sidewall height of the various tires in which you may be interested.
</edit>