I can't understand why the handbook would suggest there is no need to swap polarity between gas/no gas operation.
If an inverter MIG also has Arc welding capability, there will be two front-panel Dinse sockets, positive and negative. With gas and solid wire, the work return lead ( Earth clamp ) will be plugged in to the negative. For gasless flux-core wire, that cable would be unplugged and inserted into the positive socket.
In addition, internally, the brass block of the Eurotorch socket will be connected by a cable, or a flat copper busbar or braid to the back of one of those Dinse sockets. For gas & solid wire operation, that would be the positive. To change to gasless, that connection would be opened at the Dinse, and the Eurotorch feed cable ( only ) would be moved up to the back of the other Dinse socket - the negative. Thus only one internal wire gets moved to perform this swap. The actual torch polarity can easily be confirmed by testing with a voltmeter between the torch tip and the work return clamp; expect about 60 volts DC.
If an inverter MIG also has Arc welding capability, there will be two front-panel Dinse sockets, positive and negative. With gas and solid wire, the work return lead ( Earth clamp ) will be plugged in to the negative. For gasless flux-core wire, that cable would be unplugged and inserted into the positive socket.
In addition, internally, the brass block of the Eurotorch socket will be connected by a cable, or a flat copper busbar or braid to the back of one of those Dinse sockets. For gas & solid wire operation, that would be the positive. To change to gasless, that connection would be opened at the Dinse, and the Eurotorch feed cable ( only ) would be moved up to the back of the other Dinse socket - the negative. Thus only one internal wire gets moved to perform this swap. The actual torch polarity can easily be confirmed by testing with a voltmeter between the torch tip and the work return clamp; expect about 60 volts DC.