Personally I wouldn't bother. I would sell the 30 spline shafts and buy a set of 28 spline spares and probably have a 12 pack with the extra cash.
30 splines usually sell for more money because they are more rare. 28 splines are cheap and plentiful.
They are both the same strength since the both taper. 10 bolt axles break at the taper on outside of the splines or at the ujoint most of the time. The splines would only play a role if the axles were non necked down. So if you try and run 28 splines and keep 30 splines with you as spares for the trail it is kinda retarded.
You not only have to tear everything down to get the axles out but now you have to drop the cover to change the spider gears, reseal the diff, refill the diff, etc. Does that sound like the smart option? /forums/images/graemlins/thinking.gif Not to me. I have gotten 2 sets of 28 spline 10 bolt shafts to my door for $35 shipped.
Harley