Locking a user meta_data field from updating it

The various update_*_meta() functions are object specific wrappers for update_metadata(), which handles all meta updates for WP. You can prevent this function from doing updates through the “update_{$meta_type}_metadata” filter. If your callback returns anything but null the function returns without doing anything.

This does not prevent other functions from altering data, such as an UPDATE query run through $wpdb methods.

Yeah, how would a snippet for this look like?

It’s not clear if you intend to save user or post data. I’ll assume user. You can add additional filters using the same callback if you want to protect more than user meta. In functions.php or a custom plugin:

add_filter('update_user_metadata', 'my_meta_protection', 10, 5 );
function my_meta_protection( null, $object_id, $meta_key, $meta_value, $prev_value ) {
  // only lock "info" meta, but allow user ID 1 to alter it
  if ( 'info' != $meta_key || 1 == get_current_user_id()) return null;
  return true;
}

This works perfectly, thank you so much!