Quartus usage is really intuitive and straightforward, it's the first time that I hear a similar question. Anyway,
PROJECT_REVISION = "lphud_fpga" specifies the *.qsf file name. There's at least one revision entry in the project file. If more than one, you can select it in a pull-down field, as said.
You can click the new_revision field and a new revision name as well the previous revision where you are the settings copying from.
There's a verbose chapter about project management and revisions in the Quartus software handbook.
A drawback of the revision scheme is that global changes (e.g. adding a HDL file that's used in all revisions) must be edited in each revision separately. Or you need to set up manually a file with global settings that are imported in each qsf file.