When I'm going to lemon oil the board, I unwind all the strings at once, but I don't cut them off. After letting the oil soak in for a 1/2 hour or so, I wipe off any excess (usually none) let soak a bit longer, than restring with the old strings. A few days later, I change to new strings. I find that just after I oil the board, the strings will soon turn black or at lest discolor. I'd rather this happens to the old strings than to a new set.
Bill, tgo