I used to be much more diligent about dedicating my pipes. Strict only VA pipes, only VaPer pipes, only Latakia blend pipes and only Aromatic pipes. Burley went in whatever. But then I realized that I didn't need to worry about it.
If you have a pipe for VaPers and smoke a latakia blend in it once, after two or three more bowls of VaPer in that pipe you're not going to taste too much latakia. But if you're smoking only VaPers or VAs and then go 20 bowls of latakia, it's going to be much harder to expel the ghost. So I may sneak in a bowl of English/balkan in a VaPer pipe every once in a while and it doesn't hurt it too much. Now there are some pipes that smoke VAs fantastically and they will only see straight VAs or uncased/untopped VaBurs.
I do have some pipes that can't smoke Va or VaPer for nothing, so they get the dark leaf usually. I'm not the biggest english/balkan fan anyway so it really isn't an issue.