Can a pack of dream whip be added to already made buttercream without ruining it?

AI wouldn't. It will be grainy. Why do you want to add it?

I agree w/Annie.

I wanted to lighted the buttercream some and it was a litte too sweet. I tried some cool whip , it did lighten it but  was afraid it wouldn't  hold up .I went ahead and made another batch using indydebi's recipe. Thanks for the  help.