The following is an (outdated) article from the Guardian
Under the terms set before Tsipras, the Greek parliament has to endorse the entire package on Monday and then pass several pieces of legislation by Wednesday, including on pensions reform and a new VAT regime, before the eurozone will agree to negotiate a new three-year rescue package.
I read before that the present simple is often used for future time in a clause with before when both clauses are about the future. Is it possible to substitute agrees for will agree? If so, what is the difference in the meaning?