I do not think two tags per nation is really needed. Think about it this way. There are numerous OPMs in the game, and already several tags that are not even used.
The system would have to be handled via event but lets take France as an example. If a civil war arose, for this sake lets say a succession crisis, and the pretender is rising in the south. One of the French minors, say Dauphine would be used. If Dauphine manages to defeat France and take the French throne, an event would fire changing the tag back to France.
This would work for England, Russia, Spain, Austria, Italy, Germany, Ireland, Eastern Europe, China, Indochina, India, Central Asia, and the Middle East all have tags that should be vacant. In the case that this is not possible, then a set of generic rebel faction tags could exist where the display name would be dynamic. In the case of a revolutionary civil war the name could be Revolutionary X where X is the country name from which these rebels are rebelling from.
Also, there should be a minimum province count for where a civil war can fire.
I feel this could be entirely possible as long as some sort of flag was placed on a nation like "rebel nation" which would be the check for the tag switch.