Sorry, that makes no sense to.

To try and clarify…
When I connect modem directly to macbook, I get a browser window where I could change SIM settings.

To then connect the modem into M300, those settings need to stay with the modem/SIM.

So either modem or SIM need to remember settings right?

So when I buy a new SIM in a new country, I connect modem to macbook, setup APN settings and connect/save.

Then move modem to M300A and settings should still be there. Is this what you mean?

Thanks