Switching number associated with a phone purchased on a promotion

I have had Xfinity Mobile residential service for about 5 years now.  Several times I have purchased new phones during a promotion that required porting in a new number, most recently the Spring/Summer of 2022, then after 90 days, switching the SIM with an existing phone that I wanted to upgrade.  I would then inform Xfinity Mobile of the switch, and they would update their back-end systems to reflect this change.  Xfinity support told me, that as long as 90 days had passed since the new phone was added to my account, this was fine, and the promotional discounts continued normally through the remainder of the 24 month purchase period.

Last year(2023) I helped a Non-Profit switch to Comcast Business Mobile, and they picked up 3 new iPhone SEs on a "Free" promotion.  When they asked Comcast about switching the numbers associated with some other phones on their account to these new phones, they were told that doing so on their own(swapping SIMs) would void future promotional discounts on those phones.  They would have to take the old and new phones into a Comcast store and have a rep in the store do the swap in order to maintain the promotional discounts.  Is Comcast really preventing customers from doing this on their own now??  I can possibly see where phones with eSIMs might require a store to be involved, but not with phones with SIM cards.

Along similar lines, I have some Cellular ATAs that work great with Xfinity Mobile SIMs.  I have an older phone, that is paid for, with an active Xfinity Mobile SIM, that I just take out of the phone and put into the Cellular ATA, and voila, I can make and receive calls using the phone number associated with that SIM.  This has come in very handy when diagnosing problems or testing to see if a Cellular ATA is a good solution for a particular situation.  Would using the SIM from one of these iPhone SEs that are still being paid for, cause problems with the future promotional discounts?

Thanks in advance!