Leaking valve seals

I have a 91 eclipse and I know that the valve seals are leaking really bad and that is why it smokes so bad. I was talking to a friend of mine and he said that if we replace them then the lower half of the engine will blow. Is this correct? Or is it just ok to go ahead and replace them?

You might as well do a ehad rebuild. At least check the guides. Some people replace seals with the head on with a ton of work (including making the tools to do it). But more often than not the seals failed because of bad guides or some other problem, and the new seals go in a few k miles. Pull the head, and have a good machine shop go over it. My machinist charges 2-300 depending on how many valves/guides need to be replaced. Gasket is 60 bucks. Might as well do ARPs while you are in there for 90 bucks. If you need tbelt and friends, now is the time to change them too. Do it right, do it once ;)