Newbie question - create filter for prefixes to export and also modify bgp next hop

Hi As said, I'm new to BIRD and struggling a bit with the config syntax. I'll try to explain what I want to do. I have a few prefixes, lets say 10.1.1.0/24, 10.2.2.0/24, 10.3.3.0/24. I want to announce these (and only these) in a BGP session, but with a modified next hop. How would I do this? Any help is much appreciated. /Tias