I'll respond without reading anyone else's comments so mine are not biased by such. First of all, I don't think you'll have anything to do with the official school-sanctioned team if you go this route. I have to think others are weighing in with this opinion but my take is different from theirs. I know they consider this to be a negative. I don't. So, here's how this goes.
The track season ends. Don't say anything to the track coach. He knows nothing until track begins next year. Don't say anything to the XC coach either. If he doesn't know you exist, all the better. You must, however, talk to the new coach. This is the only person involved other than you. I feel the fact that track and XC are 2 different sports and the length of time betwee them makes this socially easy.
I made the mistake of running for the school's XC team sophomore year. I already ran, trained, raced, every, before that so suddenly being on a school-sponsored team was disappointing. By the end of high school, I certainly wasn't involved in that whole thing anymore, but there was never an awkward moment with the coach. The season only went for 2 months, so even if I ran every year, there's 10 months I wouldn't have seen the guy. The track coach didn't know who I was - we never met - so it was not socially difficult around that scene and I wasn't expected to participate.
Problem is, these guys at your school may know who you are and approach you. You may not have the lack of social pressure that I had. Here's what you do. When the XC coach approaches you and says, "Hey, practice starts next week! Are you ready?"
You say, "I'm looking into other sports. Been thinking about this all summer."
See, they assume you've still been running the whole 5 months or whatever between seasons. By track time again, if you again imply you quit running, they'll figure it's been like a year since you've run a step. They won't ask you again after that. You'll be off the hook. I mean, does the track coach go up to every fat, out-of-shape clown on campus as say, "Track's starting!"? Of course not.
You'll be doing your own thing and not be hassled by anyone at school. You'll be just another non- runner to them. It works. I did it.