I had a PM exchange with someone today on meta and after the fact would like that PM to be registered as a warning, with user note and indicator on user card and profile for future travellers. I was not sure yet when I started the PM whether a warning was warranted, but as the exchange unfolded it became clear it was warning worthy.
Unfortunately it appears to only be possible to select the tickbox to make a PM a warning when initially creating the PM. When editing the OP you cannot make it a warning.
I’m sure there are cases too when a warning PM is created but later the moderator finds out it should not have been a warning. So the ability to toggle the tickbox when editing would be helpful.