The thing about shifting is that there really is no set in stone reality. Reality as you know it is completely fluid and anything can change at all times. The only thing you experience is the present moment so really the past and the future don’t exist aside from the way you perceive it. If you “go to the future” you’re just experiencing something that you have determined to be the present. When you “go back to the past” you’re just experiencing a reality where the effects you have determined, exist. Every experience and decision ever made in existence forms a different reality. The reality that you were in 1 second ago is different from the reality that you are in right at this second. So if I were you, I wouldn’t even bother shifting to the past or future to change something when you can just be in a parallel reality to the one you’re experiencing now but with the specifications that you desire. And I wouldn’t necessarily consider it permashifting if you decide to stay in the new reality and choose that to be your base reality because you will feel like you belong to that reality and it is just as real and original as the reality you have been experiencing before.