@fBoyle-- Yes, but you should take them at the first sign of a blister, instead of taking them regularly for long periods of time. Some people do take a low dose of l-lysine tablets during winter to prevent the flu. But for cold sores, doctors recommend taking high doses of lysine at the first sign.
So when you start feeling tingling on your lip, you need to start taking the lysine right away. 1000mg/day is a good dose although I know people who take higher doses. A few days of lysine is usually enough for prevention. If it's too late and the blister has already formed, you can still take lysine during the duration of the blister to speed up healing.
But I don't think it's a good idea to take very high doses of lysine for long periods of time. Our daily requirement for lysine is very low, it's less than 20mg/day for adults. So 1000mg is a very high dose and lysine can cause side effects.