Old thread but if it can save time to some folks still struggling with this...
Here's the setup I used to remap the "Ù" key of my Canadian French keyboard to the "accent grave" key of a US keyboard (key under "ESC") to use in the Blender app (which refuse to remap my key).
The general idea of it is to make BTT change the keyboard layout to US on "Ù key down", wait 0.1 second, send the " key down" then on "Ù key up", send the " key up", wait 0.1 second then change keyboard layout back to Canadian French.
Trigger 1: your key down
Action 1: change keyboard layout to US
Action 2: delay next action (blocking)
Action 3: send key down only
Trigger 2: your key up
Action 1: send key up only
Action 2: delay next action (blocking)
Action 3: change keyboard layout back