I've been asked some questions on how i customized my sewer fight Bane. I can't track down the comments but i have answered some PM's on the subject. But i figured i would post it here.
As to how to put the arms in. Carefully take an x-acto knife and carefully start to cut the seams from the sides to shoulder and neck to loosen to glue from the top portion of the torso. Carefully work the back plate off with an eyeglasses screwdriver and do the same with the bare armed Bane. Then just interchange the arms which fit perfectly into the slots and then carefully glue the back plate back on and apply pressure until the glue holds. Then you should be done beyond a whatever minor touch ups that might be needed. Hope this helps. Remember to take your time on the final Bane figure when splitting the joints and i highly recommend the x-actor knife, watch those fingers though. heh.
Your finished product should look like so.