Depends on a lot of things. Yeast used, temperature, final gravity before addition, alcohol level, etc.
There are a million threads here about chemically stabilizing or not, etc. If it finished sweet, and maintained the same SG for say a half a year after primary seemed to be done, but just wasn't sweet enough for you - yes, you could safely add more and it probably wouldn't restart. BUT - I wouldn't go bottling an unstabilized (chemically) sweet mead for at least 1 year of absolutely NO SG change.
Brother Adams apparently said he'd see signs of restarted ferments even YEARS later, so you run serious risks if not stabilizing or very long term bulk aging under airlock.