Is it possible to edit the hotkey of an ability for an individual player?
Is it possible to edit which location on the command card UI a button appears in?
(for example I have slots 1 to 7 arrayed in a horizontal row in the bottom-center of the screen, is it possible through triggers to say button object X appears in slot 4, with hotkey 4 and but still linked to ability X?)

Note: I will want to have these command cards unique to each player - even if they are using the same 'hero' unit.
[edit] I think since this will involve setting the fields in the data editor, that I'd need to create separate units and abilities for each player - since over-riding one heroes command card would cause the command cards of all that hero unit to change - ie for different players). [/edit]

Failing all this, any suggestions on a way to implement this that doesn't revolve around the command card?

Using a dialogue is the obvious answer, but then I would have to record keypresses for abilities and come up with a clever way of showing cooldowns on buttons, etc. Also how would I get an ability to initiate through a key-press event, that allows the player to 'target' it? For example, the stim-pack ability is transient and will activate if the player simply presses it's hotkey. But for an ability like psionic storm? The key-press would have to activate the ability, and then allow the player to cast it normally (AoE cursor effect etc).

The only possibility I see would be adding every button into each command card slot and control it with validators that check for something that is set/added by triggers.

Would the triggers and validators effect only 1 unit? And not all instances of that unit in the game?

For example, player 1 and 2 both choose Hero Y. But Player 1 uses skills A, B, C and D, whereas player 2 - using the same hero, chooses to use Skills D E, F and G?

I don't think you would need to make separate abilities for each player, but you could do it by creating separate units (with all the same actors, weapons, models, movers, etc. linked) and separate buttons for each player.

As for the key press to target cast, my best guess would be that you can set up a trigger where pressing a certain key changes the cursor and sets a variable (like Psi Storm Cast = True or something). Then in another trigger, use the Mouseclick at Event with "Psi Storm Cast = True" as a condition, and then create the Psi Storm ability at the location of your XYZ mouseclick. In that same trigger, you would also set Psi Storm Cast to False, and reset the cursor.

Yeah I feared that would be the case regarding targeted abilities being activated through a dialogue. I want to minimize trigger usage as much as possible since there is no need to reinvent the wheel -IF- I can manage to get the command cards to function like Ahli described. I believe it is possible, just going to be a headache validating each ability and displaying it for the correct player unit etc. Especially since players can chop and change their command cards at will (when in Town) - and this is already achieved through a dialogue.