Well, interestingly none of the reforms I had in mind were the three you stated as most common. Barca is evidently enamoured with their Republic, for whatever insane reason that is, so Mendicant rather decided it would be a bad idea to try and force them to change, since they wouldn't accept, and making them a Monarchy, whilst still being tyrannical and corrupt would only exacerbate the problem. For banishing nobles, well of all the nobles mentioned to Mendicant, it would require banishing quite a few, since there were no clear ring leaders, also unpreferable. For changing members of the government, well that would be a pointless, temporary measure since Barca is a Republic, one that doesn't tackle the actual problems but instead is a token gesture that ultimately achieves nothing.
So in lieu of the three most obvious game mechanic supported options, we would have to choose largely player driven ones. Firstly, legal reforms to how Barca is run, and new laws enforced to prevent new occurrences of corruption and tyranny, secondly, an investigation and trial into the bounties Barca levies against its own nobles for political disputes, and thirdly, putting an end to clique mentality of the "old guard" as Julius put it, which saw newer nobles ostracised as troublemakers and traitors and had other ramifications to life in Barca.
