If a security in a model has been replaced and you wish to swap that security without rebalancing the entire account, firms utilizing the Smartleaf integration can use Specified Trades to accomplish this.
Specified trades are a type of request that enable you to buy, sell, or trade a security to its target weight, without prompting additional trading of securities from the account’s holdings. In the presence of specified trades, Smartleaf aims to recommend few to no additional changes to the portfolio's holdings. As a result, Smartleaf may make recommendations that disregard pre-existing account settings.
Full feature details: Specified Trades PDF.