Unable to enable Multicurrency Option for Foreign Currency Bank Account

For using the Promo code usage, will it impact all the Other Bank accounts (of different Business Units)in the respective environment?

Is there any option to restrict only for specific Business Unit/Legal Entity by using the PROMO CODE?

Once the Promo code is applied, can we able to reverse/revert it back to the original settings. (Presently we have both the Payables and Receivables enabled for the EUR Bank account).

In case if we use this promo code, will it affect the current bank Account Use settings