You can find the files used in the add-in from the add-in installation folder

In this case most of the code you most likely need can be found from split_and_set_spec_limits.jsl which is in bin folder.
This add-in is bit older and I would write it differently if I were to remake it. You can create workflow which basically performs the same actions:
- Split your table to get wide formatted data
- Create specification table using Summary platform
- Order of columns and their names do matter here
- Use Manage Limits to load the specification limits from the spec summary table into your split table
I think JMP is able to record most of these actions. JMP might not be able to record Manage Limits part fully, but you can check how it can be done from Scripting Index.
-Jarmo