Need help with this fastpass+ question and changing #of base tickets

[ADisneyQueen]

I have 7 day base tickets and 7 days of fastpasses already made. Now I've decided that we are doing waterparks/disneyquest so I am going to cancel one day of fastpasses ( its in the middle of my week) then go to my reservation and change my tickets to 6 day base tickets. I am more than 45 days out. I just want to make sure nothing is going to mess up my other 6 days of fastpasses. Any advise?