[Fenris447]

So I've made a little progress. Permanently removing an HD is easy enough. The feat itself does not specify which HD should be reduced. It doesn't matter in a single-classed Hero, but multiclassing means you must pick from a Wizard's D6, a fighter's D10, etc. I can either write a script to find the smallest one and remove it, or allow the player to pick which one.

Dungeonguru, you're correct about how we manipulate the amount of HD used. I found it relatively simple with your guidance. I tried it two ways. With a tracked resource, we can have the ability to roll the HD reset on a short/long rest. On a long rest, however, Hero Lab properly grants the 1/2 of spent HD back to the character but also adds back an additional hit die when it resets this tracked resource.

So a level 8 fighter with 2 HD remaining (5 were used to heal, 1 was used for the feat) will get his 4 HD back + another for resetting the feat, as opposed to the 4 total he should receive from the long rest.

The alternative is to make the tracking an Activation amount. This will persist through short and long rests, and will require the user to manually manipulate it. It's better than nothing, and it's probably going to have to be what we do.

Permanently reducing the HP should also be easy enough. Since the player has to roll to determine the amount, it will have to be a number they enter into a field manually. Unless I'm really dumb, we should be able to pull that number into a script that then takes that HP away from the max.

So I think I'll be able to have some version of this, ugly as it might be, done in time for 2.5.