depends on how well cured and how much you're adding.
What you need to be concerned about is an ammonia spike caused by any left over die off.
Are you curing the rock yourself or are you buying it (and if so, from an online retailer or LFS
if you are getting it out of a curing tank at a LFS
, it should be "ok" just ask the LFS
how long it's been in the curing tank.
If you're ordering it from online I would wait to see how well off the rock is before adding it to your main display. (have a curing setup ready as you'll most likely need it)