What date would you like the new task to reflect - the date you added it? Start date of the project? Or other date? I have run into this issue in the past as well where I set the baseline and then need to add new task(s).
I am sure Smartsheet can find a solution to this. But on a separate note maybe from a PM perspective after you set certain tasks to be your baseline i.e. your scope anything new you add will require you to revise the scope/baseline?