This is interesting, I had never considered sending submissions to agents outside my country. I have a question, though. My novel is naturally written using British spelling and conventions. If I was to submit my work to an American agent, would it be advisable to change it to US spellings and formatting first?
In my experience, agents don't mind and it's not worth the time and effort to change. Switching from British to American English is something English speakers tend to *think* is incredibly easy, but in reality there's a lot of tiny subtleties and quirks that even the most attentive writer will miss. I think it's better to write in your own English rather than try to imitate American English and risk tripping up an agent with an obvious-to-them mistake.
The BrE/AmE change can be done later by professional copyeditors at a publishing house, who are skilled professionals at localisation. There's no need for a writer to take that extra burden upon themselves when AmE agents don't mind reading BrE, and vice versa.