To remove vanilla recipes you create a recipe json file in the minecraft namespace. The file has to have the same name as the vanilla recipe file and be a valid recipe file with a result value of "minecraft:air". To add smelting, blasting or cooking recipes that output multiple items you create a "count" field with the desired value in the recipe file.
File: datapackname/data/minecraft/recipes/iron_ingot.json
{
"type": "minecraft:smelting",
"ingredient": { "item": "minecraft:iron_ore" },
"result": "minecraft:air"
}
File: datapackname/data/minecraft/recipes/iron_ingot_from_blasting_iron_ore.json
{
"type": "minecraft:blasting",
"ingredient": { "item": "minecraft:iron_ore" },
"result": "minecraft:iron_ingot",
"count": 2
}
File: datapackname/data/minecraft/recipes/iron_ingot.json
{
"type": "minecraft:smelting",
"ingredient": { "item": "minecraft:iron_ore" },
"result": "minecraft:air"
}
File: datapackname/data/minecraft/recipes/iron_ingot_from_blasting.json
{
"type": "minecraft:blasting",
"ingredient": { "item": "minecraft:iron_ore" },
"result": "minecraft:iron_ingot",
"count": 2
}