The rule with macros is you can only have “one action” per key press. So, for example, ctrl-shift-E for “drones engage” may be too cumbersome to press on a regular keyboard, so you can replace that with a macro button so you don’t have to break your fingers trying to reach ctrl, shift, and E at the same time. That’s allowed. But F1 (delay) F2 would activate two weapons, so that’s two actions with one macro button press, so that’s not allowed.
If “down arrow” and “enter” are two actions, then it’s not allowed. If you’re just trying to select a different target in the overview, something that an actual person could do with just ONE click of the mouse, then that’s possibly ok, because the “actual person” only presses the mouse button once.
Otherwise, macros that have delays are very suspicious to CCP, because people use delays when they’re trying to combine two or more actions into one key press. And also, we can’t discuss macros on the forums, but if you think about how CCP or any company would detect macros, they may have certain popular macro apps / software programs on an auto-ban list. So keep that in mind; even if your “down arrow” and “enter” are within the rules, whatever macro software you’re trying to use may be very suspect to CCP (and they may not bother or have the time to check your special case vs. all the other botters out there).
So, create a ticket and ask CCP directly what’s allowed. Give them details of the macro program you are trying to use to implement this, and what you’re trying to accomplish with your “down arrow” and “enter”, and you’ll get an official response.