HP Modification Template Question
 

I am trying to write a template that gives say a 20% boost to your total HP. Any suggestions on the best way to do that?

Not sure the mechanics, but you either need to read the hit point total and modify that.
The character has rolled 26 hit points, and their total goes up by 5.2 for 31.

Or change the die that the character rolls, potentially with a flat bonus.
The d10 is now a d10+2.

Not sure on the coding end, but you could take either approach as the basic route.