Hi,
When you set a coupon to an order in the backend, the quota is not modified.
Because you are doing a manual operation, HikaShop does not place any kind of restriction and it let you manage the quota if required.
You can specify any coupon code you want and the coupon value you want, so it does not consider that you're adding an existing coupon code (with the same rules etc).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.