customising the payment intent

Hi,
If we want to change the Payment intent , specifically the total, can we use the acton hook “simpay_before_paymentintent_created” and can we add line items here as well?

Presumably we can instatiate a particular class, What class would this be if we wanted to do this via ajax. i.e. whats our best route. Would we need to do this via create item and pass it a form_id which we have created?

Best regards,
iDigLocal