Crossposting in kbin

Crossposting can be controversial. Maybe this is a @jerry question:

Any moral issue with crossposting on #Fedia?

If not, then the next question is: how? I posted to m/Law a question about Belgian law. There was a pulldown for magazine & I chose “Law”, but I wasn’t sure if I could add more magazines separated by commas or something. So I just posted it in law. Then in m/Brussels I created an article»URL type of post & simply used the URL of the m/Law article. Seemed to work.. just not sure if that’s proper.