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.