I believe this is something what you're looking for.
<snmp-device-variables>
first_oid, 1.3.6.1.4.1.nnnnn, DEFAULT, first possible value for percent cooling
second_oid, 1.3.6.1.4.1.nnxx, DEFAULT, second possible value for percent cooling
display_variable, (${first_oid} == 0 ? “${second_oid}” : "${first_oid}"), CALCULATION, “print this in display section”
</snmp-device-variables>
Translation – if the value of first_oid isn’t 0, print the second oid, else print the first one.
http://static.helpsystems.com/intermapper/help/devguide/index.html#02-CustomProbes/snmp-device-variables.htm%3FTocPath%3DCreating%2520Your%2520Own%2520Probes%7CSNMP%2520Probes%7C_____1