It is possible. But not by much. Your best bets to decrease understeer are:
1) Bigger rear sway bar (which would also take out alot of body rolls, too)
2) Rear-biased springs.
It could possibly be that your H&R springs already are rear-biased. I don't know about BMW aftermarket springs, so you might want to check around for the spring rates on those babies. Or maybe the other members here will be able to help.
If you're overcooking it into turns, nothing you do will eliminate or reduce understeer. Remember that your suspension may increase the limits of your car, but it also very likely decreases the margin of error that you have between your maximum slip angle and wild tire-scrubbing understeer.
A forum community dedicated to BMW E46, E90, and F30 owners and enthusiasts. Come join the discussion about M performance, turbo kits, engine swaps, builds, modifications, classifieds, troubleshooting, maintenance, and more!