Remove mail/news by filters

[JackRnl]

a) After creation of filters I would like to apply them on messages 
downloaded already but can't find how
b) It would be very usefull if news I don't want to see (anymore) would 
not appear in the list. Making it 'hidden' would be great, removing them 
would also be very useful. Does anyone know how to achieve this or 
should it be posted on the 'whislist'?