Open your client files, C:\Programs(x86)\ServerName\ResItems\
Now in here you will have to find the weapon you want to edit. Look for its file to be a .Nif
Open this in NifSkope. Simply click on the model, right click on it and go Transform > Edit.
Now on the R value, set it to 180.00 to flip it 180 degrees.
As for the Odin Regi, Go to the Release section of ragezone, and look for Dev Realease Bundle v2 by NvrGnaStp.
He put a good one in there.
Hope this helps mate.