I'm making a cake, and I was just wondering, if my recipe calls for egg whites to be stirred in, could I separately beat the egg whites first to a soft peak then fold it in? Would it destroy the cake? Cause I've heard that it will maybe turn out to be a failed pavlova and I so don't want that. I just want to make the cake even lighter! 

AHope this article helps answer your question, it may not because they say to beat egg yolks rather than egg whites. It does have some other tips to make your cake lighter.

tipnut.com/cake-baking-tips/

Oh my mistake they do say egg whites not egg yolks.