Can scar-revision be dangerous ever?

Unusual: It is generally a straightforward procedure, but it has risks as do all operations. Take the time to get all of your questions answered satisfactorily before proceeding.

Yes: Any procedure can be dangerous in certain circumstances. If there is a bleeding problem the risk of a procedure can increase. If you have a heart or lung condition this can increase risk. Likewise if scar is near eye or is a keloid all may increase the risk. This doesn't mean it can't be done. Consult a plastic surgeon and discuss the risks in your particular situation.

Scar surgery risk: It is very safe to have scar revision. The only serious risks would be anesthesia related.