The panel pattern of the genoa is the critical thing.

The cloth is cut square on to the warp/weft where you don't want stretch. This is I think always on the luff. Hence on pattern has seams running at right angles to the luff. Another style has seams also running at right angles to the foot with a long diagonal seem from the tack to meet the leach.
The line of stretch being a diagonal across the cloth weave being horizontal ie paralell to the deck.
These arrangements need to be followed with the yankee.

So you need to decide if you can do it. The book by Jeremy Haward Williams called Sails is the best explanation of cut of sails. If you intend to do it yourself. You will need a very strong sewing machine however. good luck olewilll