Alternative and Supplementary routes

Top of the day, everyone!

A lot of bicycle and hiking routes in my area consist of a “core” or “main” route, one or more alternative routes that you can take if you want to take a shortcut and then some supplementary routes that will lead a bit further off the main route to some less-often seen spots.

Currently, these are mapped as a superroute containing all alternative routes and supplementary routes, but the only way to distinguish them is by name. I noticed that there is state=alternate that I then used for the alternative routes, but is there an official way to tag these supplementary routes? I’m not even sure if that’s the right word in English, but in German, you’d call them “Ergänzungsroute”.
An example would be the Kulturroute Hannover which consists of a 420km main route, several alternative routes and extra routes. Questions:

  1. Is there a way to tag these in the superrelation as main / alternative / supplementary with roles?
  2. Is there a way to tag these in the corresponding routes as main / alternative /supplementary? Using the name isn’t going to convince any renderer to treat them any different
  3. While there is symbol, osmc:symbol and wiki:symbol, there seems to be no tag where you can give an external image showing a picture of the route symbol. While I think the whole symbol-tagging should be reversed anyway (symbol:osmc and symbol:wiki), is there a tag I’ve missed that people commonly use pointing to external symbols? I’m aware that I can take pictures, upload them to the wiki and then use wiki:symbol, I’m just wondering if there’s something like url:symbol or whatever…