Manuel,
In your preflight programming you can program Star, and that is the endpoint off your route it says nothing about wich RWY.
You get the current landing-RWY by Atis / current ATC., If your online you can see this in the Atis of the selected ATC., (this info is also on Servinfo),
If the transitions are know by FMC you can program them , otherwise ask for vectors. (mostly you get vectors form ATC)
Example : at EHAM EELDE 1A Arrival star Looks like EELDE-NOVEM-ARTIP
ARTIP is the end off your Star arrival (Holdingpoint(IAF), After this point you fly a Transition and RNAV to the current RWY,
eg ARTIP-2B transition RWY 18R looks like
ARTIP-EH600-EH601-EH603-NIRSI-EH607-EH608.
Transition is a fixed route from holdingpoint(IAF) to startpoint of RNAV apprach, you don’t need radarvectors to intercept ILS.
In above example NIRSI is start point off RNAV approach.
And if your already on approach you can always select another ILS Freq by hand , but I think that's a little late,
Regards , Willem EHM1328