The moment you give notice to your broker to exercise @ the $4.75 price, you have purchased GBRC shares at that price independent of what 'retail' is at that time. If retail was $5.50, you could instruct your broker to exercise the warrants and then sell immediately at the $5.50 price (market or limit order) and pocket the difference.
If you do not exercise them within the expiration time period, the warrants become worthless. KP