There are different kinds of keys for different purposes and encryption systems.
Which keys are you referring to? For which encryption system(s)?
And which kind of card are you talking about?
Assuming you are referring to goldwafer files, 99% of filesets on the net consist of a software file for the 16f84 PIC and a key file for the 24c16 EEPROM. So to incorporate new or changed keys only the eeprom file needs to be edited and reprogrammed. However, if you are talking about a wafercard with non-removable chips, the eeprom is only accessible via the PIC (through-PIC proramming) - so although only the eeprom's contents need to be changed, that still requires first programming the PIC with a "loader" and after programming the eeprom, putting the original PIC file back again.
Also be aware that different versions of the PIC software support different numbers of providers, so it is not always possible simply to add more keys. You may have to replace a key instead.
Finally, some PIC software supports the updating of keys via the parental-lock feature of the receiver once the card is inserted.
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