Possibly. On other platforms, aMule has a feature called the Tray Icon or Tray Integration. Among other things, it provides a pop-up menu with several choices, including the ability to change aMule's bandwidth limits.
The problem is that this feature doesn't work well on the Mac. It causes aMule to crash.
Of course, that's a problem we (I) really ought to fix, but... uh.. erm... I haven't.

Mind you, I haven't actually tested recently to be sure the crash is still there. It's remotely possible that changes in wxMac and/or aMule have spontaneously fixed it, but I doubt it.