[inquisitor]

Won't they be deleted automatically? I think my Swiss IMSI had disappeared before I renewed it last week. Also I didn't pay attention whether the current IMSI is actually a new one or if I was re-assigned the previous expired one.

In any case I guess deleting an IMSI manually is not that easy as you will need to hack the STK application on the SIM card, which probably cannot be downloaded from the SIM card so it can't be reverse-engineered making such undertaking even more complicated. Perhaps you would need to inject a faked OTA update to delete an IMSI which is also quite challenging, as I expect such to come encrypted.