Scenario test by varying inputs or by modifying the model?

When solving a policy / strategic problem - I have typically thought about exploring the different policy options as a scenario planning test where policy options are different inputs. Is this how others think about this? Or would you solve for the right inputs as its own optimization? i.e. if I’m trying to solve for the best place to put a recharge station for an EV, should the possible recharge stations be varied in the input and run through a scenario test? Or should I build an optimization model which takes in the demand for charging stations and outputs the optimal locations on a map? And if the answer is the second option - how would you do this? TL;DR - should I scenario test by varying inputs to a model or by modifying the model to do it for me?