There is no need to change anything on the dish/lnb - the signal still comes from Astra 2A.  The only down side of the freesat boxes is that the EPG (electronic program guide) isn't as good as the Sky one. The advantage is you get more channels and all the BBC and ITV regions without having to add them in (as you do on a Sky box) so if you start losing your picture due to adverse weather you can change to a different region and will hopefully still be able to view the program.

Nigel