No. Discount codes on Cryptohopper can only be applied at the time of your first purchase. If you already have an active subscription, you can't use a discount code to lower the cost of future invoices.
What this means for you
First invoice only — Your discount code applies to your first invoice only. Starting from the second invoice, the full subscription rate is charged.
No retroactive discounts — There is no way to add a discount code to a subscription that is already running.