Torrello,
The forbidden list (generally) can only easily be managed by the unit, there might be a series of AT commands using CSIM and CRSIM which can clear it but I am not sure of them right now. The FPLMN elementary file is defined as having 3 fields and is FIFO based i.e. one gets written to the top of the file the one at the bottom drops out.
Re the signalling and writing erroneous networks to it, the unit will only write to the field if it receives a specific rejection cause from the network, if the attach attempt is incomplete due to interruption’s, BER, etc this would not result in a rejection with a specific cause but be written off as failed hence the field will not be written to.
Regards
Matt