
Well knowing Fetts skills in espionoge/sabatoge/ect. he could enter the federation and use manipulation, politicol pressure, and down right brute force (nothing like roughin up your superioirs for a promotion) to get to the top of the politicol food chain,he woudl be a very infulential voice in the government, there he coudl do many many things:
1.) Begin convincing his superioirs to cut back on its military expenses, medical supplies, ect. and promote futher exploration into scientific areas (whatever, you know "catalouging gasous anomalies" or something) by suggesting that they are drasticly more powerful than the empire and need not waste time on barbaric military practices.
2.) Sabatage, draw up designs for "improved" warp reactors that shoudl eb fitted on each ship-but of course with a flaw one can exploit, whether it be a bomb in the system (probably not though) or some sort of weakness when hit in a specific area or when given a certain command. Make sure as many ships as possible are fitted with these new warp reactors and exploit them at the feds moment of weakness (at the begininng of a battle or whatever).
3.)Assasination, obviously just what it sounds, find the key member sof the federation, the ones that make its gears turn and kill them in the least suspisious way possible (poison is obviouly the most likely candidate for the job) and watch as the federation crumbles.
In short Fett could single handedly (ok not quite, he might have a few contacts but whatever) defeat the feds from the inside which is fine by me caus ein my opinion he already won, coolness factor prevails!