Can a new doctor fill out an Army Line of Duty form after reviewing medical records?
I'm not sure what you mean by "new doctor"? In any case this can get really complex so before you make any decisions about stepping outside what your command wants to do, you should do your due diligence and learn what you face. The form itself isn't clear but appears to lean towards someone who knows your current status well.
Then we have the regulations that cover how decisions about LOD injuries are made...you knew there'd be a policy & procedure manual, right?
This is where things get complex PDQ so do your homework. When we're on active duty it's sometimes easier to wait until after our honorable discharge to argue fine points about our medical condition. If we have the evidence we need, the VA often rates us much differently (a higher % than what DoD had awarded) than what we were told at discharge and as difficult as dealing with VA can be, it's easier than dealing with an obstinate active duty command structure.