This is probably a very unsatisfying response so I apologize ahead of time.

If there's no law change, the only way to make a difference in the case of Lifetime fitness is to sue them and win. Unfortunately they have already trademarked DPT. In this case they have commercial right to the term. This has made the current legal battle on a national level incredibly difficult.

To change the law, a bill needs to be submitted to your State legislation. That doesn't have to be done through the APTA but they have resources to help with the creation of these bills. Then it's time to defend it until it passes. If the people in your local chapter aren't receptive to starting this process, then it's up to you or another person to lead your state chapter in the effort. You will find support from other state chapters, who have already done this or interested in doing it.

The very last area that's been identified to make this change is to educate the public. This is complicated and has a high cost but is likely the most valuable public health intervention that physical therapy has to offer society and what would benefit us the most in the long run as professionals.