I'm not sure I understand what you're asking...
Is this a 5 axis head that can be added to a 3 (or 4 or 5) axis mill?
Or is this a permanent set up (i.e. rotary axes are always present)?
1) Added when needed case
Set up a separate 5 axis post & link to main. Use Method /"Head" UDE tto switch posts.
In the fourth/fifth axes pages of the "machine tool" view, just set up appropriate offsets.
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled
It is best to have the control handle head and tool compensation. For Fanuc - that is G43.4. If that is not an option - I am not aware of out of the box code to throw an offset for a twist head. There are (however) math routines to help.They can be found in ugpost_base.tcl in the POSTBUILD\pblib directory - this file is souced in for every PB post.