Currently: you have to upgrade a whole new set of 9 diamond shovels to netherite, to make the netherite vanilla+ tools
In order to make vanilla+ tools upgradeable so you can keep enchantments like all other vanilla netherite tools, I suggest making a
[ diamond hammer/shovel + block of netherite --> netherite hammer/shovel ] recipe for the smithing table. This keeps the upgrade cost at 9 netherite ingots, but the upgrade process is more vanilla-like, and you dont have to create a whole new hammer/shovel
Currently: you have to upgrade a whole new set of 9 diamond shovels to netherite, to make the netherite vanilla+ tools
In order to make vanilla+ tools upgradeable so you can keep enchantments like all other vanilla netherite tools, I suggest making a
[ diamond hammer/shovel + block of netherite --> netherite hammer/shovel ] recipe for the smithing table. This keeps the upgrade cost at 9 netherite ingots, but the upgrade process is more vanilla-like, and you dont have to create a whole new hammer/shovel