You are not the first person to ask for this however since each person has a different idea of what the simulation should be. I doubt you will find what you are looking for.
One client I am working with wants a what-if that is more crashing the schedule and it would have to be adjustments to selective tasks. Another one tells me that want to get a what-if on if they have endless resources. Someone else I know wants what’ifs on increasing all resource availability by 1 hr per day.
What i would do is take a copy of the schedule, set a baseline into baseline1 to get the picture of what you started with. Then make all of the changes you need. Then set the baseline into baseline 0. Look at the Multiple Baseline Gantt and see the difference.