That depends, is it possible that what you have is an early HG with UG threading? (easy to spot as they have the internal threads for the HG lock-ring as well as the external UG threads.
If not then it is possible to make UG sprockets fit by filing the wide spline but you'd still have to find a threaded sprocket for the small spot.
Easiest solution (assuming your hub is compatible) would be to get a HG freehub body to replace the UG one with.
============= Sig =============
Just a y2k FSR with some modern bits