Opencart Mod Expert Needed

I have an opencart site 2.102 that needs to be updated to the newest version and all product data to stay there. The opencart has some hard coded code done by someone to give me functionality the cart needs. (the custom functionality allows you to add tables within a product where you can add skus, descriptions, stock, low stock, weights, and options with stock count to each table row) The current functionality needs to be redone to work in a mod so no core files are changed. I also need additional functionality to allow bulk discounts to work when combining quantities from multiple products within the same category. There will be a few categories that this will need to apply to.... so category A will allow you to combine products with products within category A... Then category B will allow quantities to be shared within category B.... All categories will not be sharing quantities. <<< so this needs to be set up somewhere saying these select categories can share qnty... If you have a better method of doing this like setting up groups or something... I am open to anything that can work,,, If you would like to see the site please message me...