問題なく言えますよ。
未来形?will be,do /be going to be,do の時と違い、基本的に未来完了形の場合は入れ替えて言えます。ほとんど意味は変わらないです。
例 ・You will have perfected your English by the time you come back from the U.S.
・You are going to have perfected your English by the time you come back from the U.S.