Is there a word for a change so small that it doesn’t seem to be a change at all?

Today, I was reading an article on pharmaceutical companies making minute changes to a drug in order to extend the patent. In one instance, the company profiled did not actually change the content of the drug, just the outward appearance. This got me thinking, is there a word in the English language that means “to change without changing” or “a change so small that it’s not a change at all”? I thought about the word superficial, but that doesn’t seem to fit.

English doesn't get much more precise than this...

Infinitesimal — immeasurably or incalculably minute.

It gets a bit mind-boggling when infinitesimal amounts are involved in, for example, homeopathic remedies that are so diluted there's only a very low probability of even a single molecule of the original substance being present. Which to me means an amount so small it's not actually there.

EDIT: I can't resist pointing out this answer itself now embodies an (almost) infinitesimal change. It was recently amended (not by me) to add a space before the first word. But you don't see it because of how the ELU display works (I only twigged by looking at the edit source).

A phrase I might use is a negligible change, which is often used in the Sciences to mean a change small enough to be ignored.

However, in the context of Science, a negligible change can be noticeable - it's just so small that it won't affect the system or experiment. Therefore, this might not be the word you're looking for.

I’m not aware of a single word that has that meaning, but you might try the following descriptions:

• a cosmetic change (a change that only affects appearance)
• a trivial change (a change that has no significant impact)

Imperceptible is very close although it can speak more to the perception of the viewer of the change more than the change itself.

How about an "inconsequential" change? eg: "a change inconsequential, except that that it allows them to extend their patent"

or, "technically inconsequential"? eg: "a technically inconsequential change, but one that allows them to extend their patent"