Suppose you have Apple Remote Desktop (which, it turns out, is a very nice administrative application if you have more than 2 macs to manage, or if macs that you manage are across slow net links). Suppose you need to connect with it to a Mac where you didn't enable it in the System Preferences.
This is how you do it:
1. ssh to the machine (you *do* have to have sshd enabled, AKA "remote login")
2. run this command:
$ sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -activate -configure -access -on -restart -agent -privs -all
This will enable ARD for all users on the machine. Now you can connect in and fine tune whatever you want.