Well it is a bummer to have all that extra room but if you can't go back and return them or get new shoes in anyway than I guess you'll have to just use them. I'd do something to fill up the space so your foot isn't sliding all over, it won't really matter if it effects the break in, and I don't think it will. Instead of tissues you can get little heel things that stick on to the back heel of your shoe so it pushes your foot forwards instead of stuffing the end

Regardless of the sport, an ill-fitting pair of shoes will cause problems. You should exchange them for a proper fitting pair.

If the shoe is just as your foot, then your football will be better, Professionals make there shoes just tight so the preformance would be better. And it will take you time to adjust and play.

Point is that it will affect your football!! If you just play for fun then it's O.k but if your serious about it, then..........

It will affect your play. I suggest you have shoes that fit your foot.

They are called FOOTBALL BOOTS and the bottom of a FOOTBALL BOOT are called STUDS or BLADES!

I recently bought Adizero F50s, turns out they were 1 US size larger, it fits nicely and all but the problem is a gap in the front, I filled it with a tissue and it fixed the problem, But would that affect the cleat from breaking in and molding to my feet?

off-topic question (answer not needed but would be appreciated): Should I do the hot water trick?