A while back I discovered that the Flight Plan Route Description dialog can be used to store multiple routes, if you leave at least one blank line between them. I keep route lists for several tours in the dialog and just copy/paste the desired route pair at the top of the dialog followed by a blank line. You can do the same with full-route flight plans from SimBrief but it's a little messier. You can even do "Load From Flight Plan" and it will only overwrite the content up to the first blank line.

Yep. The lines below the first one are a scatchpad. Normally the first one is highlighted but it is hard to see in dark mode.

Also see https://www.littlenavmap.org/manuals/littlenavmap/release/latest/en/ROUTEDESCR.html for details.

Alex