"You can surely get a mid length rear derailler and a much larger cassette. It would be helpful to know if you're on SRAM or Shimano.
That said, you can't be getting much use out of that 48 up front for cross racing. Even the pros are only…"
"Are you running single or double ring? If single any Shimano rear derailleur will fit a 32t rear cassette.
If you cut the chain to the right length*, have an adequate chain keeper** and good dismount technique you'll be fine with any…"
"Yeah, no problem. Having a spare bike seems to be a thing of the past for most races such that the pits are largely empty outside the pro ranks and some super supported juniors and masters. There will be space for you somewhere. Good luck!"
"The pits at nationals work like any other pit. If you don't have someone there you can still leave wheels or a bike and affect your own repair. Having someone there just makes it faster, easier, and means someone can hand you a clean bike every…"
Funny... I had a 42, single ring, in 2007. Always felt I wasn't able to keep up on the road sections, and wished I had the bigger ring. Went to Nats and got outsprinted (for 27th...) Went to the 46/38 for 2008 and had one of my best seasons ever. I've been thinking of going to a 44/36, though. Been struggling a tad this year with the climbs. Got married, took time off, had family in town... and it's all crashing down now!
See you on the start line somewhere along the way!