Solved Custom Anvil Repair Cost

I'm making a system where you can repair items infinitely in an anvil with a cap 30 lvl at max. I looked into the resource https://github.com/Geeveloper/MaxRepairCost. this kind of does what I want but uses methods that cause warnings in the console which I try to avoid at all costs.
Warning

Code (Text):

>WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by me.abandoncaptian.pluginName.Events.Anvil(file plugins/pluginName.jar) to field java.lang.reflect.Field.modifiers
WARNING: Please consider reporting this to the maintainers of me.abandoncaptian.pluginName.Events.Anvil
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

I just want the anvil to check if the repair cost is over 30 and if so change it to 30.

 

Actually I got it working,

Code (Java):

@EventHandler(priority = EventPriority.HIGHEST)
    public void anvilCost(PrepareAnvilEvent e){
        if(Main.repairCostNerf) {
            Player p = (Player) e.getViewers().get(0);
            AnvilInventory inv = e.getInventory();
            if (inv.getRepairCost() > Main.maxRepairCost){
                Bukkit.getScheduler().runTask(pl, ()->inv.setRepairCost(Main.maxRepairCost));
            }
            if(Main.maxRepairCost > 40) {
                if (inv.getMaximumRepairCost() != Integer.MAX_VALUE) {
                    try {
                        CraftInventoryAnvil anvil = CraftInventoryAnvil.class.cast(inv);
                        Field container = CraftInventoryAnvil.class.getDeclaredField("container");
                        container.setAccessible(true);

                        Field modifiersField = Field.class.getDeclaredField("modifiers");
                        modifiersField.setAccessible(true);
                        modifiersField.setInt(container, container.getModifiers() & ~Modifier.FINAL);

                        Object containerAnvil = container.get(anvil);
                        Field maximumRepairCost = ContainerAnvil.class.getField("maximumRepairCost");
                        maximumRepairCost.set(containerAnvil, Integer.MAX_VALUE);
                    } catch (NoSuchFieldException | IllegalAccessException ex) {
                        ex.printStackTrace();
                    }
                }
            }
            if (inv.getItem(0) != null && inv.getItem(1) != null && inv.getItem(2) == null)
                p.updateInventory();
        }
    }

 

when u mad, u mad

 

I tried that originally but it didn't seem to work, so I took this route.