Using Styles with Unequivalent Outlines

I’ve become frustrated trying to build a template that is styled nicely, but that has a different range of Headers needed in the different elements of the outline.

For instance, part 1 requires Headings for Levels 1-3, and paragraph text at Level 4.
For Part 2 of my document, I need Headings for Levels 1-2, and paragraph text at Level 3.

Is there any way to create a template that works within this construct?

I doubt there is, but thought I would ask.