Hey Macaron35- fantastic writeup/mod.
A couple questions, as I was in the same boat as you (and moreso now that I've modified mine to be larger)- and resorted to a similar modification of the hips (I made small struts for the knees) with another hinge piece. Even out of the box the AT-AT would never stay in any position except straight up/straight legs. I have solid legs and hips....
However- I am having issues with a solid attachment between hip and body, would you please provide a couple more pictures and/or discussion of the attachment? I'm utilizing 4 attachment points per hip (3 blue pins plus long brown from the set, layered within the 2 hinge and filler piece section) but there is zero confidence in their stability/integrity.
Thanks!!