Using the deseed command you can use a deseeded version of the wallet file to move it to the online computer, make transaction and then bring it back to the offline machine and seed it again.
Thank you for your answer. I couldn't find any documentation on this procedure, so I would ask you to clarify it please.
So in the bash console of the offline computer I type
$ electrum -o -w wallet1 deseed
Then take the deseeded wallet file (wallet1) and copy it to the online computer, from the online electrum open the wallet1 file and make a transaction, close electrum.
Then take the wallet1 file and copy it back to the offline computer, open it in electrum... and how do I reseed it ?
Please correct me if I'm wrong, I'm trying to figure this stuff out but can't since there is no documentation.
Thanks in advance.