add_filter(
    'mastodon_api_parametrized_routes',
    function ( array $string_list ) {
        // Your code here
        return $string_list;
    }
);

apply_filters(
			'mastodon_api_parametrized_routes',
			array(
				'api/v1/accounts/([^/]+)/featured_tags'  => 'api/v1/accounts/$matches[1]/featured_tags',
				'api/v1/accounts/([^/]+)/following'      => 'api/v1/accounts/$matches[1]/following',
				'api/v1/accounts/([^/]+)/followers'      => 'api/v1/accounts/$matches[1]/followers',
				'api/v1/accounts/([^/]+)/follow'         => 'api/v1/accounts/$matches[1]/follow',
				'api/v1/accounts/([^/]+)/unfollow'       => 'api/v1/accounts/$matches[1]/unfollow',
				'api/v1/accounts/([^/]+)/statuses'       => 'api/v1/accounts/$matches[1]/statuses',
// ...