Just in case anyone comes looking here, the possible solution to the above is to use:
modprobe ixgbe allow_unsupported_sfp=1,1
As in: you have to spell out allow for both ports in the case of an 82599 NIC for example.
It must seem obvious to most since it's barely mentioned anywhere but hey... modinfo DOES say it's an array Image may be NSFW.
Clik here to view.
| parm: | allow_unsupported_sfp:Allow unsupported and untested SFP+ modules on 82599 based adapters, default 0 = Disable (array of int) |