Question about adding to existing discount promo

[DisneyGuess]

My 14 & 16 year old boys had decided they weren't going on our upcoming trip. Now they are changing their minds, maybe. We won't be 100% positive until mid-January. I had already bumped us to 1 room at POR from 2 rooms at Pop on the SPD promo. I know the booking for that ends 12/31.
If they decide to go, we'll need to go back to 2 rooms at Pop. Can I switch back to Pop & add another room & 2 kids to our existing package & they still be covered under the SPD rates? Or will I have to forgo that discount for them & hope for the new one to be decent?

ETA: This may be the wrong spot to post this! I cross posted in the Resort Discount board, so this can be deleted if so.