[dungeonguru]

This is a hack you can copy to your personal .user files to play with. It presents a dropdown of the hit die pools that are attached to the character and adds 1 to the pool chosen. It looks a bit weird, because if you have a 5th-level Druid/1st-level Barbarian it shows as a list with 1d12 and 5d8. If you choose 5d8, it adds a single d8 to the In-Play tab going from 5 to 6. Long Rest seems to work correctly (1/2 the trkMax rounded down is restored).

This hack doesn't change the hit points you have and doesn't change the number of hit die that the 1st level class has though, you still have to add hit points via the existing hit point adjustment.

You can't change the actual number of hit die on a class first level that I can see, so you have to just work with an In-Play hack on that die pool tracker to simulate it. Every time I tried to change the hit die at 1st level, it changed the hit die for all levels so I had a 2nd level Barbarian with 4d12 hit points if I added 1 to the actual class hit die. Luckily the tracker on the in-play tab is derived and independent.

<thing id="pXXXHitDie" name="Hit Die" description="Select this adjustment to add a hit die of the selected type to the hero." compset="InPlay">
    <fieldval field="pCandExpr" value="DiceSize.? &amp; Helper.HitDieShow"/>
    <tag group="Helper" tag="NoIncr"/>
    <tag group="Helper" tag="AdjNoPlus"/>
    <tag group="ChooseSrc1" tag="Hero"/>
    <tag group="OthAdjCat" tag="Misc" name="Miscellaneous" abbrev="Miscellaneous"/>
    <eval phase="PostLevel" priority="10000"><![CDATA[
      ~ If we're not enabled, get out now
      doneif (field[pIsOn].value = 0)

      ~ Add to the chosen hit die
      field[pChosen].chosen.field[trkMax].value += 1]]></eval>
    </thing>