How to differentiate keyboards ?

Hi !

I just download BetterTouchTool to check whether it can be helpful, and so far I need advice.

System :
MacBook Pro early 2015, under Mojave 10.14.6

What do I need ? :
With the help of an additional keyboard, to reprogram any touch from the additional keyboard with a function equivalent to a sequence from the main keyboard.
For example, say I want to create a "copy" touch.
So pressing the "A" touch belonging to additional keyboard provides same result as pressing the "cmd+C" sequence on the main keyboard.
So doing, I can make a customised keyboard to work with technical software provided with a lot of shortcuts.

What did I do :
(same example : pressing "A" touch on additional keyboard have to provide copy command)

1/ In the preferences menu I chose "keyboards shortcuts" in "all apps".
2/ Clicked to record a shortcut ==> "A".
3/ select action
4/ chose "record shortcut".
5/ ==> "cmd + C".

Result :
Works fine (in a same way as a macro recorder does), BUT both keyboards work the same. In other words, I cannot use no more the letter "A" on the main keyboard, because instead of "A", it gives a "cmd + C" sequence like the additional keyboard does.

What is the mistake I did?

Thank you, regards.