The Shopify FrontEnd uses this to update the metafield validations:
{
"operationName": "MetafieldDefinitionEditMutation",
"variables": {
"input": {
"visibleToStorefrontApi": true,
"pin": true,
"namespace": "custom",
"key": "primary_collection",
"validations": [
{
"name": "choices",
"value": "[\"Horse Shelters\",\"Sheds & Storage\",\"Livestock Shelters\",\"Chicken & Hen\",\"Kitset & Cabin\",\"Lifestyle\",\"Horse Paddock Shelters\",\"Equine Accessories\",\"Sheds & Storage\",\"Garden Sheds\",\"Small Sheds\",\"Wood Sheds\",\"Wood & Tool Shed Combos\",\"Green Houses\",\"Large Sheds\",\"Pump Sheds\",\"Potting Sheds\",\"Pole Sheds\",\"Workshop Sheds\",\"Outdoor Storage\",\"Farm Sheds\",\"Pig Stys & Shelters\",\"Livestock Paddock Shelters\",\"Bobby Calf Pens\",\"Chicken Coop\",\"Large Chicken Coops\",\"Small Chicken Coops\",\"Portable Chicken Coops\",\"Hen House Accessories\",\"Chicken Feeders\",\"Raising Chickens\",\"Kitset Cabins\",\"Playhouses\",\"Studios\",\"Pitched Roof\",\"Carports\",\"Boat Sheds\",\"Garage\",\"Bach Sheds\",\"Summer House\",\"Sleepout\",\"Kitset Garage\",\"Portable Cabin\",\"Pitched Roof Cabin\",\"Chicken Caravans\",\"Chicken Runs & Fencing\",\"Chicken Coop & Hen Houses\",\"Goat Shelter\",\"Alpaca Shed\",\"Shed Conversions\",\"Liveable Sheds\",\"She Sheds\",\"Lean To Sheds\",\"Tool Sheds\",\"Run In Sheds\",\"Loafing Sheds\",\"Settler Stables\",\"Hunter Stables\",\"Custom Horse Stables\",\"Shelter With Tackroom\",\"Upland Garden Sheds\"]"
}
],
"name": "Primary Collection",
"description": "",
"ownerType": "PRODUCT"
}
},
"query": "mutation MetafieldDefinitionEditMutation($input: MetafieldDefinitionUpdateInput!) {\n metafieldDefinitionUpdate(definition: $input) {\n updatedDefinition {\n id\n description\n name\n pinnedPosition\n validationStatus\n invalidMetafieldsCount: metafieldsCount(validationStatus: INVALID)\n validations {\n name\n type\n value\n __typename\n }\n __typename\n }\n job {\n id\n done\n __typename\n }\n userErrors {\n message\n field\n __typename\n }\n __typename\n }\n}\n"
}
However, the Admin API using the same mutation & input types throws an error when you include the validations field.
Also, outside of the definition:
https://shopify.dev/api/admin-graphql/2022-07/mutations/metafieldDefinitionUpdate
https://shopify.dev/api/admin-graphql/2022-10/mutations/metafieldDefinitionUpdate
https://shopify.dev/api/admin-graphql/unstable/mutations/metafieldDefinitionUpdate
Maybe we can get this added?