Request: 5E Houserule (HP on level) -- First ever FGU mod

I'm brand new to scripting with Fantasy Grounds, so I'm hoping this isn't an overly complicated thing to ask...

I want to implement a global house rule for the campaign I'm starting next Monday. Please note, that I would like this to function as a House Rule and either have the ability to toggle it in the options, or function like an extension if that above is not possible. I have not idea how to do this.

What it does
Changes the threshold of HP gained by a factor of 1 for each level after 1st. Gives a chance for +1 hp per level.

How it does it
Forces rolling of HP after 1st level. If the result of the die is 1, the die explodes once. The HP gained is the result of dice rolled.

Example
Tordek (Dwarven Toughness, Feat:Tough, +2 Con, d10 Hit Die). Tordek advances a level. His Player rolls a 1 on the hit die causing the die to explode once (bonus die); The result of the bonus die is also a 1. His player notes the new HP gained as 7 (+2 from rolled HP, +1 from Dwarven Toughness, +2 from Feat, +2 from Con)