OP - I understand about the Dolphin and the double beds.
If modifying to Pop, 1 night with the 8-day tickets, Swan for 6 nights and then POFQ works for you and your budget, it's not the end of the world (I mean, yeah, being at Swan the whole time would be great, of course!). I would just ask your TA if she is modifying reservations or re-booking? If she is modifying, you don't need to worry about your existing FP+. If her intention is to cancel and re-book, I would book anything new first, link everything to
MDE, make sure everything is showing up correctly and then cancel whatever you don't want. It means dealing with new deposits and refunds, but I've personally never had an issue with WDW or Swan/Dolphin issuing refunds on cancellations done within the proper time periods.
Again, I would also see what is currently in the Gift of Magic inventory for you dates. I'm not sure what your budget is or what you are currently paying? Both CBR and RIV are showing in that discount inventory and have access to the Skyliner which makes getting to EP and DHS really convenient.