How can I set it up so I can use a single key for multiple functions?

I want to set it so that my D key does ability 4, and also inventory 3, and my F key does ability 5, and also inventory 4. And respectively to do "take and retrieve items" on courier.

When I try to set D to ability 4, it will stay as take on crow, and F on ability 5 will stay as retrieve, but when I put D and F on inventory 3 and 4, it'll take D and F off of everything else, and only be used for the item slots. I plan on just not using slots 3 and 4 with active items on heroes with 4th and 5th abilities, such as doom, and I know it's possible because I've seen Sing Sing do it on Rubick, and he had D set on a Inventory slot for an item, as well as his stolen skill.

I asked a similar question, and you can find the answer for both setting multiple keys to one action and one key to multiple actions in there.

Set 2 buttons to same action