Infrequently used build agent license question

I have a question about licensing of build agents.  Does a disabled agent consume an agent license?  Can I have more agents than licenses, and manually enable/disable them as needed?

Our situation is we have 4 agent licenses (3 with enterprise license and 1 more).  We want to add a 5th agent (a Mac, not that it matters).  One of our original 4 agents is used infrequently (like once in the last 5 months), but it must remain as it is the only machine that can run a particular build.  We'd like to just disable it until we need it, freeing up a license for the Mac.  Is that allowed?

Thanks,
Josh