As far as I know, hot vinegar forces a kind of patina on a blade, and mustard and hot vinegar a particularly mucky looking patina.

It is only a surface thing, and as such any rust-proofing is very minimal. Usually the patination is promoted by a combination effect, some things used are salt water, hydrogen peroxide and hot vinegar. Note that the acids must be neutralised and the patination 'sealed', often with oil, to stop active rusting.

Etching is not the same as rust proofing, as any basic google search will tell you.

If you want to increase the effect of patination with regards to rust control, you get into the russeting/browning/blueing camp - although not particularly complex, these processes, if done correctly, take a lot of time and effort. Stronger acids and alkalis are used, carding (combing) off the rust and re-rusting after boiling is used, except in the brown processes, as boiling converts the red active raust into pasive black rust, the basis of bueing. Hot salts and or fuming are used - these processes are markedly more durable than those bought in bottles and applied cold.

Regards,
Neil