While an external preprocessor would without a doubt improve performance, I would suggest you PM a dev regarding SOE's position in this regard.
Since your preprocessor would have to process game data and pass it back to the interface during runtime, they might wave the EULA at you which has some provisions in this regard.
But if you explain to them that all your preprocessor is doing is perform the same functions that can already be done via UI modding - only much faster - they may make an exception.
Just don't get yourself banned so shortly after your return.
