My two cents would be to add 1/2(5/8 to be more exacting) to the length of the shaft. Reason being that this would not change the weight distribution of the head. However you might want to recheck the loft/lie as shaft length has an impact on that. You can always choke up or remove the extension to go back. Removing lead and cork can be difficult.
Here are some of my thoughts, Weber. If I wanted to add 4 swingweight points to my clubs I’d consider one of the following: 1) adding weight and a cork down the shaft, 2) adding a half inch extra length to each club (1/2” = 3sw pts.), 3) pulling the shafts and redoing the swingweight with tip weights, 4) using lead tape on the back of the heads. Of these options I’d be most inclined toward the lead tape because it gives the best performance even though it messes up the appearance of the clubs. It’s also a great first step to be sure the new swingweight is right because you can easily undo it. Since you’re using a lighter graphite shaft, adding a 1/2 inch may also be an option. Most clubmakers build graphite shafted irons a half inch longer than steel because of the lighter weight (38-38.5” 5 iron). I wouldn’t consider hot melting. Simplest way other than lead tape may be #1. I’m sure you’re familiar with all these options, but I’m chiming in! Hope these thoughts help! Cheers! Michael