It is on the settings page, and, in theory be ticked/unticked. But, from a PPM perspective, a program should only have milestones, not a full schedule as these should be in the children projects for example. Try it first in a non production environment.
Also, though you can have portfolio / program / project, this doesn't follow the underlying hierarchy in PPM. I'm not saying what you doing is wrong but a portfolio in PPM is a completely different module. If you were to stick to the PPM hierarchy, it would be Program / Project / Sub-Project,where the relationships is then driven by inv_hierachies. But just my view, as for example, I have added additional portlets to portfolio to show things like issues/risks for the investments that make up the portfolio as an example of bringing additional data into the portfolio area.