From Wikipedia:
[EEPROM] is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration tables or device configuration.
Most components (such as RTC) uses them to store their configuration (do an interrupt everyday at eight, for instance).
You may indeed reprogram it (to set the alarm for example). The difficulty of it depends on the device and the support available for it, of which you give no information whatsoever.