Is one button hero swap into ability possible?

What I want to happen is the following:
Button press > Change to Genji > Dash > Change back to original hero in one button press

Yes, but it would not be instant. It may help to preload Genji though.

Yes, it’s pretty possible

Rule 1:

Condition
Is Button Held (The Button)

Action:
Start forcing player to be hero (GENJI)
Set player variable A to TRUE

Rule 2:
ongoing- each player
all
Genji

COndition:
player variable A == True

Action:
Press Button (Ability 1)

Rule 3:

Condition:
Is button held(Button) == True
player variable a == True

Action:
Start forcing player to be hero (your previous hero)
Stop forcing player to be hero (your previous hero

If you want to change back to the previous hero instantly, add a wait action upon switching to genji and then switch back to your hero,