Send shortcuts of US-keyboards

I would like to remap CMD + "+" or CMD + / to some other key comb, because with the Swiss German Keyboard I can't send it natively and many apps don't recognize the surrogate CMD + shift + 1 key. I've tried to record a keyboard action with BTT, but it doesn't work, as I can't do the CMD + "+" combination in the first place!

Analogous I would also like to send CMD + [ resp. CMD + ] combinations.

How can I do it?