Making one part of model with more infill than another

I have a square based model that needs to have the ability to be leveled. My thought was to put countersunk screws in each of the four corners that could be extended, as necessary, for leveling. To do that I figure I'm going to need a solid or near solid piece of plastic to be able to tap for the screw threads (not to mention just having that area around the screws sturdier so they don't strip out after a few uses). The issue I'm having is that it's not practical to print the entire model with 100% infill nor would I want to. Are there any methods anyone knows of where I could set certain areas of a model with different infill than the others?

I haven't used it yet, but the current Slicer 1.1.7 lets you have different slicing parameters in different regions. I suspect you can do what you want with that.

That's a great tip, Roxy. I'll check it out.