Would that be possible to the extent that I could add on crystals (not change color crystals though)?

Shimaon

You want to upgrade swords with crystals.
Why would you want to do that? when you can just make a sword uprade with vibration cells, bonding alloys and energy projectors.

I think if you really wanted to make a sword upgrade with crystals you could, but it would involve alot more work than it would to just make a new upgradable sword.