modify custom data attribute in custom recipe (1.21.1)

I have an item that uses the minecraft:custom_data field to store information. I'm trying to make a custom recipe that modifies this information by adding a specific value. I feel like I have a basic understanding of how the custom_data and attribute_modifiers work, but I'm struggling to get them working together.
some more information, if it helps:

the recipe involves Create contraptions, but afaik that shouldn't change the data format for the result item
I'm trying to increment the tagStock custom data field by 100 each time the recipe is completed