It depends on what you connect on the WAN side - could be a DSL modem, could be a cable/docsis modem, could be lte modem, ...
I think the OPNsense forum is the wrong place to ask such a question - it would be better to contact the vendor of your modem!
If the modem is locked then Opnsense would not be able to access it either. Opnsense is at its basic sense just another computer with an in and an out.