I am assuming your are speaking of the AC cable. If so here are my thoughts.
The cable is attached to the frame and into the Gen Set. Therefore to lengthen the cable you might need to put a water proof box in the location where the cable is attached.
Put a 90 degree water proof connector on the gen set and add enough new water tight conduit to give you the correct length as to be able to move the gen without putting it in a bind. You will also need a longer cable (12-2/ground or matching what is there now) from the gen to the box. When you put it in a loop be sure that it doesn't rub or snag on something else.
I hope this helps. I can see it in my mind and hope I have presented it properly.
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