It's not too hard to make changes, but it's by trial and error.
you set the hap to open with notepad.
Then, here is the first line of the "stand.hap" (make a copy of the original, so you don't mess you only one up)
(there are a lot of different parts, just showing the first as an example)
setreg [ figure=fullBod name=RThighForward f0=0.0000]
If you change the value of 0.0000 to 1.0000, her right thigh will move, when you save the changes, and drop the modified hap file in the console.
The value can be a negative value, like -1.0000, or -0.2500, etc.
Sometimes I have to add setreg values that are not there, like if there wasn't a LThighForward, I'd add it, if needed.
The Hardest part is getting the fullbody girl to change from a standing position, to another position, without having to readjust the position of the body with the mouse. I cannot do that, yet.