"Sticking" a Category for a Permalink
I have my permalink structure set to /%category%/%postname%/. This works very well when a post belongs to 1 category.
For cross-referencing, I'd like to set a post to more than 1 category. The documentation says that %category% takes the lowest number category.
What does "lowest number category" mean?
How can I force a post that is in more than one category to have a fixed permalink based on a specific category of my choosing?
Is there a way to renumber categories to get the effect that I want?