MIB files contain the meaning of the given values of SNMP OIDs, practically telling you how should you interpret those values. Zabbix should be able to handle these values, know their meaning. It could either be done directly from the MIB files, or by telling them within templates.

From templates, extending the XML scheme would be simple, like:
<values>
<value data="1">Signal Lost</value>
<value data="2">Locked</value>
</values>