Letter Tracks? I think you may mean Letter Trim? The plastic edging around the Acrylic Channel Letter Faces?
If so, you can hit the joint with a little of the Weldon glue that is used to adhere the letter trim (the watery stuff). For about 3 seconds, it will soften the bond and you can remove it. Work in sections of about 10-12" around each letter. Then, please, use the old letters only as a pattern to make the customer some new faces so we don't suspect you're a hack.
Good luck.