The PRGN_CUST tables contains entries for a number of switches which can affect the default behavior of various security transactions. To move away from the default behavior, we need to create the entries for the switches with the appropriate values. The list of allowed entries keep on changing depending on the version of SAP being used. Hence, the best way to find the allowed list of values for your system is to open up the table in SM30 and try to enter a new entry. A search for the possible entries will display the allowed entries and also the SAP notes which describe their use.
The screen below, gives some of the possible entries for a system on SAP R/3 4.7.