As with most beurocratic agencies, your outcome is 100% correlated to the mood of the customs agent. Get one that just wants to check your papers and go along your way?… you’re good. Get one that has questions that he/she probably already knows the answer to and is waiting for you to lie, good luck!
If you put it in a normal bike travel case, you’ll be absolutely fine. Have it new, still in the package, may raise some eyebrows
I know this thread is about something else now, but FWIW I once declared a bike on my blue customs landing form thinking it would be fine since I used it where I bought it before bringing it into the US. Turns out it needed to be older than 3 or 6 or 12 months or some length of time, so I got hit with an import fee. Was like $85 on a £1000 hardtail in 2014 iirc. Entering at Newark and headed to Chicago.
Thing is, they couldn’t find the cashier to ring me up so after about 10 minutes they just let me go and ripped up the paper. I suspect they would have preferred I didn’t say anything about it in the first place.