What you enter in the comments box will stay in comments box but it may not matter.

When the hotels prepare the rooms they know the status of each guest based on other data in the reservation. So Golds/Diamonds staying at a Hampton get the water & cookies, etc.

When I make a stay with a higher status than I had when I booked the stay I usually show my card at checkin. It generally won't make a lot of difference if you check in as a Diamond and the reservation record shows you as Gold since the systemwide perks don't differ much. There may be local exceptions where the property extends a courtesy to a Diamond that they wouldn't to a Gold. I've seen parking fees waived in the US or lounge access granted overseas for Diamonds only. In most/all cases showing your new status card at checkin should get you what you deserve.