Well, like I said, it ain't kosher, but it will work.

If you switch out the main, there may still be an issue with neutral ground loop current being generated, but any lineman worth his salt is going to take appropriate steps to safegaurd against such stray currents anyways, or they ought not be doing that sort of work. I am no lineman, but I do know to check any circuit and isolate it before working on exposed leads. I am pretty sure that is something not only taught to but required of anyone who intends to earn a living working on electrical supply systems in this country. If the lineman do not take such precautions, well, I won't go so far as to say they deserve what they get, but they will get to learn the lesson the hard way I suppose.

There may be some issue with certain control/safety devices in the wiring that might not like all that AC load, but I can't think of any configuration that will trip unless the power limit is exceeded, which based on the initial criteria ought not occur. If it were a DC circuit, I would worry about diode isolation or maybe a crowbar SCR circuit protection or some such, but about the only things you can do to protect AC circuits is GFCI or current overload vis-a-vis fuses and circuit breakers, which don't care which direction the source comes from. What little resistance/inductance coupling might be in the wiring between the generator and the ground retrun is probably insufficient to establish stray ground loop or voltage division anyways, unless you are running an extension cord more than 30 feet away from the gen to the outlet.

There are inherent hazards in using my suggestion. It is a survival technique in case you find you have not prepared in advance by adding the hard wiring to your household circuit for such an event. It is easy to do it the right way if you have the materials, equipment, knowledge, and time to do so. If not, then the extension cord method is as simple and easy as it gets, and can be deployed in less than a minute.

If you are concerned about frying the lineman, make a checklist and make the first step switching out the main before lighting off the gen, and the last step switching the main in after shutting the gen off AND uplugging the stub.
The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)