welcome to the Plugin Café and thank you for reaching out to us. Please read the Forum Guidelines for future questions. This is a forum about the development of Cinema 4D plugins and scripts run by Maxon to provide support for developers. Requests for scripts are not within the scope of the forum, and when they must be posted, they should be posted under General Talk.
I therefore have treated your question as a programming question. Please also note that we, Maxon, cannot provide full solutions.
The primary misconception of yours is that objects and vertices (or UV vertices in this case) would have an implicit unit as for example centimeters or meters. But they do not, all units you see in the interface are only an "illusion" for the end user. The data itself is unitless, e.g., an object has the width of five units, and not a width of five centimeters (although the interface might display it in that form). The same applies to UV islands, there are no UV-islands with the size 5*5cm, there are only UV islands where the UV-vertices all lie in the interval [0, 5] on both axis, i.e., a "5*5 units" UV-island.
You can manipulate UV vertices directly by reading and writing from a
c4d.UvwTag or use
c4d.modules.bodypaint.CallUVCommand to invoke one of the existing UV commands. We have an example for
CallUVCommand on GitHub.