Actually, slippage of one day is already there. Since it is not possible to initiate a transaction on the same day when signal occurs, backtesting always use a 1 day slippage. If your question is regarding making it configurable then yes it can be done. As of now it is not present.
I have taken a note regarding slippage and transaction cost. May be in next update which should be released in a month or so we will have this.