Don't box yourself in, what if you have change of heart the night before rank lists are finalized? Now you've overpromised and there was no need.
I made a very last minute change of my rank order right before lists were due.
Some of the residents that I had be-friended from different programs had inquired re my ROL which I shared with them.
Then I had some last minute indecisiveness regarding my ROL.
i felt compelled to stick to what I had previously said for sake of integrity. for a short amount of time, I even felt a twinge of regret for, as Jitter Bug put it, "overpromising." Not that I was seriously considering changing my ROL, but I felt that I had cornered myself into a decision.
this turmoil didn't last long, and thankfully I did not make any changes.
To the OP, you were going to tell your #2 program, that they were number 2 in your book? imagine telling your significant other, something like that, and imagine how that would go over...
I don't think that programs want to hear "you are my number 1" but I do think they want to know which applicants are seriously interested. I have been part of the interview process for the internship at my program. when we sat down to review all the applicants, my PD went through the applicants that had expressed interest in our program first. (it helps when you have to go through 10x the number of applicants per spot)
conversely, we also really appreciated the applicants that wrote us and said that they were withdrawing from the match, or were only applying to categorical programs.
I hope no one wants to bump into a PD/interviewer at a conference and be remembered as the applicant that wrote "you are my #1" but didn't match at their program.