I made a Cheat Engine thing for Freezing/Increasing/Decreasing the HP for Hikari, Aya and Ichika.
The hotkeys are:
6 | 7 | 8 : To increase the HP of respective character when they are down on the ground
y | u | i : To decrease the HP of respective character when they are down on the ground
h | j | k : Increases HP of respective character
n | m | , : Increases HP of respective character
x | c | v : Freezes HP for respective character
"z" is used to freeze/unfreeze the HP of all characters when they are down.
I didn't test this extensively but it worked for me even if I restarted the game.
Which character that the hotkeys are attached to depends on how they programmed this game, either it is attached to the slot that the character is currently in the loadout or it is actually attached to the character itself.
The version I am running is the GOG 1.33 with the R-18 patch applied and I wouldn't expect this to work on anything else.
After some testing I can see that the pointers I use for the hotkeys are not consistent, I'll have to look into it some more