hey, i'm a second year joint honours student. happy to answer any queries.
yeah, you choose your elective modules before you leave, which i thought was a bit sucky as well. i missed out on latin fast track because i spent so long umming and ahhing.
if you can, try and choose from the elective module handbook asap, as a lot of popular modules get full up v. quickly. however, it's not the end of the world if you're not happy. they hold elective fairs on fresher's week where you can go talk to people from your elective department, or enquire about others. also in the handbook they should've provided emails for people responsible for those modules if you have any questions.
and, even though it is quite a bit of hassel, if you really CANNOT STAND one of your electives, and have managed to find another maybe in sem2 that you'd rather do. a lot of my friends did this last year.
hope that helps! x