[MENTION=84680]treex[/MENTION] What would be your reasoning be behind trying to cause a mutiny, apart from Themes being a pirate?
To be honest the question has me a little worried.
In any case I think your chances are less than zero. No one on board knows you or trusts you. The one person that liked you was the captain. The boat ride will last less than a day so you won't even have a chance to win the crew over. Like I said right from the start, this is not a boating adventure.
Besides, who in the PC group would support your mutiny? I very much doubt that anyone else in the group would have even the slightest motivation to go along with such an act. In fact some of the characters have a vested interest in not getting on the wrong side of the Count and so would more than likely actively stop you.
Your character is of course free to behave however you think he should behave. The friendly peg legged Captain who idolises the Lah'nun ... well that was to help you motivate Themes to get on board with the adventure. To some degree you have chosen to reject that. Fair enough. Your choice. I guess you are imagining them as in conflict with the Count, where as I am imagining them having reached a mutual understanding and even a happy co-existence. The Count is certainly not as straight laced as you perhaps are imagining him, and the Captain is not a straight laced military officer.
This is my first time as DM in PbP. It is not however my first time DMing. I'm quite happy to let players play their characters how they see fit. And I'm also absolutely fine with giving realistic reactions to PC behaviour. That means if you want to play Themes as a PC who dares rob the most powerful man in the Crystal Isles who has connections throughout the underworld who has no qualms in killing those that cross him ... go for it. But Themes will not be safe just because he is your character.
If we were playing a sand box campaign where the expectations are that anything goes, or even a campaign of any description, you might find I would give you a different answer. But that is not the case. It's not even a campaign. It's an adventure. The adventure is what it is. It's a published adventure which I am adapting a) to fit the setting and b) to try and hook your characters into it. I don't have the time to write my own adventure. Sorry.
So I guess you either get on board with it or don't. Best to decide that before the ship departs.