Can we (or should we be able to) rename Power-ups?

Sometimes I change the name of a Power-up Rem by mistake, then quickly fix it.

Does this affect the power-up’s functionality? Does it break anything?

Regardless, considering these are special Rems, should users be even allowed to edit/change them? Or should we at least have an option to restore original Power-up names? (Could get confusing in the future, as we have more users and more Power-Ups.)

No.

The data-rem-tags have a different name. So when you use specific CSS that relies on the specific name it will not work. But many powerups are identifyable by different means as well.
And you have to be careful when you want to paste something (Pasting formatting with Power-Ups Rems).

Otherwise you are free to change the text since RemNote works with the rem id, not the text. And I think flexibility is good.