Custody agreement question - flexibility for summer

So our custody order locks us into a pretty rigid 50/50 split during school year. Kid wants to do a 2 week soccer camp this summer that would mess with the normal schedule. I asked my ex if we could swap some days around and she said we'd need to modify the agreement formally. That seems like total overkill to me for one month. Can we just agree to something in writing via email or text and skip going back to court? Neither of us wants to spend money on lawyers again but I also don't want to do anything that screws us later legally.