What's the process to add a new tag if you're under 300 rep. For example I want to add "arcgis-10.3.1" but I'm only 186 rep. Do we open a chat with a moderator, or add a comment on the post, or is there another method?
I think the preferred way to coin a new tag before getting to the reputation needed to do that would be to add a comment on the post. Flagging a moderator to add it is also possible but I think coining a tag would be borderline when flagging is meant to be the course of last resort.
In this case I, for one, would be very likely to make a tag of arcgis-10.3.1 (if one appeared) become a synonym of arcgis-10.3 because we gained reasonable consensus a long time ago in Tagging ArcGIS questions? that we would not go more fine grained than dot releases of ArcGIS products.