I've never understood the taboo on blowing out candles when doing these spells. Nobody I've talked to has ever been able to give me a particularly good reason for it (or rather, their reasons depend on their particular metaphysics that I may or may not agree with). I don't usually do it simply because I use very small tapers when doing candle spellcraft, but on occasion I use a larger candle with the intent of burning it over the course of several days. I blow them out. It's never been a problem.