Here's where it gets complicated. If your project is an entire UI replacement, you are going to forget what I said about setting the scale of a frame twice. In this case, you would want to use
Code:
myFrame(SetScale(UIParent:GetEffectiveScale()))
which is the same as 1/newScale/newScale. The truly complicated bit at this point is that you will have to constantly adjust myFrame's height or width and possibly SetPoint in your pixel perfection function each time the user adjusts myFrame's height or width.
For the record, it would best to
not offer adjusting the scale of a frame in your project's options, and only offer height and width as options to keep your sanity, along with enforcing your new scale.
Pixel perfection is a truly massive undertaking, but the results can be beautiful if you put the time and effort into making it work correctly.