I know of a couple examples of bus swaps (does this not take place in Downpatrick?) As I said before the 252 service involves a bus swap between Coleraine and Larne due to the time taken to operate this service between Coleraine / Giants Causeway / Larne etc and on to Belfast. The bus which is most often swaped in this case is CL Goldliner 525 (PXI 5525). A change of driver in LR between a CL and LR driver would be quicker than all the passengers moving from the CL bus and onto a LR bus. Other examples that I can think of off the top of my head are one of the services between CL and LD which involves a bus swap in Limavady. Again instead of the passengers changing bus, the drivers change bus - this is why Tiger 460 (HXI 460) of CL is often seen operating Derry City services for example. I think there is also a swap that takes place between OM and LD during an early morning express service and V and LD. This would explain why LD ends up using both Great Victoria Street and Omagh Goldliners on express services such as the early LD-CL via Limavady (234service) As is the case with MF and BM who change bus on one of the 127 services between MF and BM, as Martin said this change takes place in Portglenone. I am sure there are many more examples of this but these are the only ones I remember. One thing about this swap of buses, is that a large amount of pieces of A4 Paper is used for desplaying different destinations, as a OM bus for example does not have LD destinations such as Coleraine express.
------(A picture of Tiger 460 during its express days is available on www.homestead.com/busesinpictures)