Hey please can someone help me?

I'm creating a creature mount and my game is crashing when I select ride. I know I need to add a Saddlebone into the skeleton.nif but how do I do that?

Really appreciate any advice help and tips

Is this what I need?

http://skyrim.nexusmods.com/downloads/file.php?id=3790

Am I able to somehow export the skeleton.nif file from the Creation Kit, open in NifSkope, add the saddblebone, then import back into the CK?

Please advise

I can probably figure out how to add the bone etc, but could someone please tell me how I can make my creature use the skeleton nif file I make?

I'm very new to all this