Motivated by the love of Christ, Paul works and flexes and adapts where he can to relate to where people are they are at. If they are under the law, he becomes as one who is still under the law. He's not under the law, but he relates to them as if he still is. Then to the one who has no law, he relates to them as if he wasn't under the law. He's not being disingenuous - he can relate to those under the law and he can relate to those who aren't under the law, so he just changes his focus. He's flexible for the sake of reaching people with the saving message of Christ.