When I do that, I start with clean file, count the strokes until I get the weight I want, and the file the rest with the same number of strokes, starting each one with a clean file. The first one will take you a couple of minutes because you need to stop and weigh until you get it right. Once you have it down to the right weight, it shouldn't take you more that a minute each for the rest, including cleaning the file. No matter the condition of the file when you start, lead is soft enough to do the job quickly and easily.
I would surely rather invest 30 minutes to get 24 jigs the right weight than invest the cost of getting a modified mold.