Extra material on selected surfaces

[Warshef]

Let's say I have a complex part which needs precise dimensions on certain surfaces, and I want to achieve it by machining it on a milling machine, for an example I have a cube which needs one width to be within 0.02mm tolerance, then select those surfaces and tell the slicer to add like +0.5mm extra material, basically pulling the surface out by that number, and machine it to final size later, and leave the other surfaces as it is

Adding the option to all 3 axis would be the best if it's possible

[JohnOCFII]

This option to increase size by percentage or by mm for any or all axes would seem to meet your desires. Just click on the lock icon to change a single dimension if you don't want to change all 3 by the same amount.

[Warshef]

This option to increase size by percentage or by mm for any or all axes would seem to meet your desires. Just click on the lock icon to change a single dimension if you don't want to change all 3 by the same amount.

Scaling will enlarge the entire model, I only want to pull out certain surfaces, not scaling the entire model

[neophyl]

That is the task of CAD software not a slicer. In CAD you can selectively increase the areas you need to machine to tolerance.
I know people love to have one tool for everything but please lets try and use the correct tool for the job.