Station resourcing try to allocate you a group that's close to where you live though usually it ends up being opposite to where you live. It's quite common on the underground for new starters and those having gone through promotionals so take that as it may.
Cover groups consist of the station group your assigned to plus other groups that you 'could' work in during your cover weeks (sort of like relief weeks where you'd cover other shifts on your groups e.g. cause of annual leave, absences or other reasons). In most cases, depending where you are based, groups try to keep their staff covering stations in their group rather then sending them off to cover other stations in the cover group. And there is a whole system to this which will be explained to you via the Framework. Note that it is the group you'll be wanting to swap and the cover group along with it.
As an example - You were allocated West Ashfield Group which consists of West Ashfield Station & Kensington Down Street Station (a Zone 1 Group). Your cover group is District City which consists of your group (West Ashfield Group) + 4 other station groups.
Now the answer to your question; It is possible to swap station groups and in the first instance it would be within your training class by mutual agreement. If however no one is able to swap with you then you'll have to stick with it for a year minimum (6 months probation then you can nominate then another 6 months till you are allowed to move but this may be longer depending on waiting lists for each group).
Hopefully that clears up a few things. Let me know if you have any other questions.
