I put extra supplies for HMP.
Remove some enemies for HNTR without having the extra supplies I added for HMP.
With both of these difficulty settings implemented that way it turns ITYTD into a combination of both HMP and HNTR; it has HNTR's lesser enemies and ITYTD's double ammo and health hard-coded stat, similarly to how extra supplies were added for HMP.
If I can think of something creative like disabling teleporting monsters or moving a key around I'll do that too.
If I ever make a mapset, I'll rename the difficulty settings to represent what's been changed.