hi guys,
i just noticed that on the DEP/ARR menu in the fmc, there is, once you choose a SID odr STAR, the appropriate runway and the respective TRANS noc chance to change the choosen items.
As far as i know, the lowest LSK on the left side should provide an "ERASE" funcitionality. Currently, there seemes no way to change the values you have choosen, only via leaving the ARRIVALS/DEPARTURES page and call the page up again.