Edit ability across subdivision levels

Primary, secondary and tertiary shapes are an important cornerstone of art, particularly when it comes to sculpting.

Here is my proposal.

A modifier that is essentially a modified subdivision surface, except, by using a slider, an artist can switch between subdivision levels on the fly.

An artist may, for example, while working on a high res model find that the primary shape needs to be changed. He can go to the base subdiv and do so and come back up. This has the advantage of not leaving noticeable digital brush marks that appear when a high res geo is moved beyond an extent.