Multiple Quartus releases on Linux - How to choose from command line

I'd say avoid putting both paths at the same time. First, it won't work as expected, and second, users could have weird results.

One solution could be putting two small scripts in /etc/skel, one for each Quartus version. Each newly created user will receive copies of them in their home directory (or just copy for already existing users). Then upon login the user would "source" the preferred version's script from $HOME.

And it's not just about paths, there are some other env settings that Quartus expects. Local copies of the scripts are good idea, so each user would modify to their needs.