I only make fruit jams, and I use the inversion method to seal them (pour screaming hot jam into hot, sterilized jars, whack on the lid and screw it down tight, invert the (painfully hot ouch ouch) jar for five minutes, turn right side up and wait to hear the lid go "ping!" as it cools and the contents contract). This method used to be described on the jam instructions in the pectin box, but now is not there - presumably because somebody decided it isn't safe. I have used it for years, frequently with re-used lids, and have NEVER had a seal fail. I would only try this with something that is entering the jar at a crazy hot temperature, that has a high sugar content (inhibits growth of yuckies) and which I will be able to hear go "ping!". Since I don't can I don't know if any of that applies to other stuff.
Alison