A friend of mine also lost the end of his reefing line down inside the boom, but unlike on my B36(2002) which has a boom end cap that is relatively easy to remove, on his boat, a Dufour 40 or 41 built in 98, the boom end cap is riveted on. Fortunately here in North Wales whilst there is a thriving sailing community, the riggers are not snowed under with work and pretty much need whatever they can get and so they keep their customers friendly. Having lost his reefing line, my friend went to the guy in the rigging workshop at the yard where our boats are laid up for the winter, for some advice. The rigging guy followed him back to his boat, retrieved the lost reefing line in less than ten minutes, and all for no charge at all. Result one very happy potential customer.
If your guy doesn't want to know, I can only guess he has too much work and doesn't need every customer he can get.
PS I don't think it matters too much if the reefing lines are on the wrong side of the boom, so long as you know which of the rope clutches deals with which reefing line and you mark them accordingly. It might baffle others who sail with you, but on your boat you can set the system up as you want it. However, with the end cap off, you could if you wanted put right the mess that your rigger left and remember not to use him again if you have the choice.