The Store Credit funds do not have an expiration date as these are real money on a customer's account that are simply displayed in the Store Credit section of their account at the store.
The work logic of the module can be changed by modifying its core files. Mirasvit provides an unobfuscated source code for its products, and allows for customizing extensions according to
the needs and requirements of its extension buyers. However, the company does not provide such a service, and recommends that you use help from its partners.