Edit the .ini files with a text editor (wordpad should work).
found in the C:\Users\%username%\AppData\Local\SWTOR\swtor\sett ings or whatever it is for you. Try editing client_settings.ini and Graphics_Mirror.ini to have the correct values for your resolution. The reason why you can't change resolution is because it prompts you to accept, and gets to your changed resolution too slowly to make a response, thus reverting to your original resolution.
This worked. Thank you so much!