There really are no "must" mods. But depending on your needs, you may want to add heavy duty tuners. I think the tuners are the weakest part of the SX basses.
Actually, from my experience, the stock tuners work VERY well as far as holding tune. In nearly 3 years of gigging with the stockies on my no.1 the only time it's ever come out of tune on a gig is when a guy physicaly slammed into the headstock, and turned the tuning key.
I tend to play pretty darned hard, and I'm more likely to break a string than have the bass come out of tune.
