Editing imported legacy FBX in unity editor

Hi I've been trying to modify an animation in Unity's Animation window, but it's marked "Read-Only". The imported FBX adds it's own rotation to my player which I don't want because this is a top down game and the rotation makes him run forward while the he's facing left. I'm able to delete the rotation of the FBX file while it's readonly which corrects this problem but every time I re-import the game the rotation gets reapplied and the problem comes back. How can I make this change permanent?