I'm sorry, I did not see your photo before my first response. Having looked at what you want to do, I agree with the other responders but already I see that the leech has been stretched as I described in my first post. The change you will make will pull down the leech even more and will stretch the leech more. This will result in the leech "motorboating" which is a self descriptive term arising from the sound it makes when the stretched part starts flapping at high speed. This can be fixed in several ways when it occurs: you can make small "darts" in the sail seams that will take out the stretch; add some cloth up the leech to strengthen it; cut out the stretched part ; or make a new, purpose built sail. The other ting I did not mention before is that many jibs have a leech line sewn in to help prevent this and to adjust depending on wind strength.

I would just go ahead and do what you want, have fun, and then fix or replace the sail when you are ready.