I'm currently trying to implement this, but I think it can only be manually done (edit your own IMSI numbers in smscon_code file). Smscon can't do it automatically because it doesn't know if one of your cards is a valid card when swapped the first time. Possible solution: at boot time press a specific key to learn smscon the new SIM card (save new IMSI code as valid in smscon_config file). Don't know if this can be done...