Replace any Minecraft ingot with a diamond

The following loot modifier will replace any Minecraft ingot item with a diamond:

{
  "actions":
  [
    {
      "type": "loot-table-modifier:entry_item_set",
      "name": "minecraft:diamond"
    }
  ],
  "predicate": {
    "type": "loot-table-modifier:entry_item",
    "name": {
      "regexPattern": "minecraft:.*_ingot"
    }
  }
}

Explanation

The action entry_item_set replaces the item in an existing matched item entry.

The predicate entry_item matches specific item entries based on their IDs. It can match using a regex identifier, which allows using regex patterns.
The regex pattern minecraft:.*_ingot will match every item that has an identifier that begins with minecraft: and ends with _ingot. For example minecraft:iron_ingot and minecraft:gold_ingot will both be matched.