Not sure if this is the best way to do it, but you can modify the player.lua file (found in Scripts/entities/actor/ folder).
If you look at the Stance section of the file (near the top ish) it will look something like this:
Code:
stanceId = STANCE_STAND,
maxSpeed = 4.0,
heightCollider = 1.25,
heightPivot = 0.0,
size = {x=0.41,y=0.41,z=0.3},
viewOffset = {x=0,y=0.065,z=1.65},
weaponOffset = {x=0.2,y=0.0,z=1.35},
viewDownYMod = 0.05,
modelOffset = {x=0,y=0,z=0.0},
name = "stand",
useCapsule = 1,
If you change the size's Z parameter from 0.3 down to say 0.2 then that will make the character short enough to fit through a standard height door. You can try fiddling with the other values as well but it might take some trial and error until you get something that works the way you like it. Also note that you may want to change the values for the other stances as well (crouch, swim etc) depending on your needs.
