Alright, so according to the properties.lsx, Male Henchman use the following RootTemplate-
23f3af72-437c-4aff-91ca-914ef6e6ebb7

While Female Henchman use this-
3ec36a84-93a1-409f-83d6-4b7b17745df6

Which RootTemplates (and consequently, what Stats) do those correspond to?

Females
RootTemplate- Companion_F_Kickstarter
RootTemplate GUID- 3ec36a84-93a1-409f-83d6-4b7b17745df6
Stats- Henchman_Madoc_Paladin

Males
RootTemplate- Companion_M_Kickstarter
RootTemplate GUID- 23f3af72-437c-4aff-91ca-914ef6e6ebb7
Stats- Henchman_Jahan_Mage


This makes changing their default stats (including "CriticalChance") quite simple; you just need to overwrite the two Stat entries with a mod. And maybe change Madoc/Jahan to point to a copy of their original stats, if you're wanting to preserve them.

At some point I might try to figure out how to get custom henchman via a mod rather than making a Main folder directly.