HP Edit box able to override TEMPLATE imposed Hit Die percentage

Some description is required please, e.g. syntax in use.

Half Hitdie HITDIE:%/2|CLASS.TYPE=Monster VISIBLE:NO
Quarter Hitdie HITDIE:%/4|CLASS.TYPE=Monster VISIBLE:NO
Eighth Hitdie HITDIE:%/8|CLASS.TYPE=Monster VISIBLE:NO

Apply that to level one creature, imposes the HD, but not quite...

Define "not quite"

If the HD is not equally divisible, then there are steps taken to try to turn it into a real die. So are you trying to do d6/4? What specifically is the math being attempted, what is the incorrect result, and/or what doesn't work.

Okay, so HITDIE:%2 - takes a d8 and makes the value a d4, correct?

Well, what it seems to do is half the possible outcome, d8 1-8 becomes d8 1-4 possible. I can go into the HP dialog box and reinstate the value of 8.

Thus, the HITDIE is easily bypassed. (Also, if you tell it to re-roll, the roll ignore the HITDIE restriction.)