I said it would be fine didn't I? I'm not that much of an offset nazi am I? It will be undectectable the difference between 46 and 48 unless you were doing repeated testing for an extended period. Your suspension might wear a little more too but is that really that significant? If your shocks wear out at 74k instead of 75k are you going to cry? Yeah, didn't think so. Offset is important but it's not like there's 100hp lost for ever mm...
I just get on people's case that don't understand it and buy rims without really thinking it through. They usually end up complaining here that something's wrong with the car when really, it's just with them.
Also, autocross is typically about 90 seconds of hard driving. It's hardly going to boil your break fluid.
Oh, you can decrease offset with spacers (which would worsen your problem) but increasing it is much more difficult but neither is in your best interests.