I'm not sure what software you're using, but if it's Combat Minion, just substitute the default crit letter code for your weapon with the Large or Super Large crit code. Eg. Change 7BS to 7Bwh if attacking a Huge creature.
Note that the full list of crit codes are given in a link on the Attack Result panel, ie. the same place you're entering the "wh". For convenience, I've pasted them below:
ROLEMASTER COMBAT MINION - Crit Code Abbreviations
Critical code abbreviations used in attack results are shown below. Attack results format is <hits><severity><critcode>. Hits must be given, even if 0.
Eg #1: "15Cst" is 15 hits and a "C" Martial Arts Strikes critical.
Eg #2: "0Bco" is no hits and a "B" Cold critical.
Eg #3: "15Dth" is 15 hits and a Mithril Weapon crit again a Super Lge Creature.
LARGE/SPECIAL CRITS: You may override any Crit result in the attack form by typing in a new result. This is especially important for crits against
Large creatures and special attacks such as mithril, holy and slaying. Simply replace the original crit code with any other crit code found below.
Melee Crits Elemental/Arcane Crits
G = Grappling co = Cold
K = Krush el = Electricity
P = Puncture he = Heat
S = Slash im = Impact
T = Tiny mn = Mana (Arcane Comp)
U = Unbalancing vo = Void (Arcane Comp)
aa = Aether (Elemental Comp)
Martial Arts Crits an = Nether (Elemental Comp)
st = MA Strikes di = Disruption (RMCIII)
sw = MA Sweeps
br = Brawling (SS/FRP only) Holy Crits
sb = Subdual (SS/FRP only) hw = Holy Weapon (SS/FRP only)
lk = Locking Holds (MA Comp) hs = Holy Spell (SS/FRP only)
nv = Nerve Strike (MA Comp)
Large Creature Crits Super Large Creature Crits
wl = Normal Weapon wh = Normal Weapon
sl = Normal Spell sh = Normal Spell
ml = Magic Weapon mh = Magic Weapon
tl = Mithril Weapon th = Mithril Weapon
hl = Holy Arms hh = Holy Arms
yl = Slaying Weapon yh = Slaying Weapon
ll = Slaying Spell lh = Slaying Spell
