I read the OP was asking if you could run a DOUBLE MALE 120VAC ILLEGAL hookup PLUG to PLUG extension cord and plug one MALE end into the Inverter and other MALE end into an existing 120VAC Receptacle which would back feed all the other 120VAC receptacles. This is where folks are calling this a dangerous and ILLEGAL procedure.
Maybe I read it wrong...
I use the standard extension cord here on my 600WATT PSW Inverter with one drop going to the home entertainment cent and the other drop going to the bedroom area where I have a few must have items ON all the time. I also have a 120VAC RECEPTACLE close to the Shore Power connections where I can plug the Shore Power Connection using an adapter to be powered by the INVERTER. This requires me however to flip a bunch of circuit breakers in the Power Distribution center before doing this since my INVERTER is not large enough to run the whole trailer.
This is my OFF-ROAD POPUP floor plan showing how I would be configured using my INVERTERS...

Roy Ken
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