Hi..
Program RIEQUI20->include MIEQUI20->line no.2450.
Here you can find a enhancement-section.
What enhancement section for is, If customer do an implementation for this, it overrides the standard code.
So you create an implementation for this Explicitenhancement section and put the whole code existing in implementation DIMP_GENERAL_MIEQUI20(line no.2603 to 2775).
Now you add your new selection variable in where condition of the copied code.
Afterwards this select query is going to execute.
Regards
Sreekanth