Double clicking a spot swatch in the Swatches Palette allows you to rename the swatch. In past versions, Illustrator would not allow you to rename the spot swatch if it was used in a linked or embedded image. Now the spot swatch can be renamed whether or not it is used in an image. There is no warning that the spot being renamed is in use. After renaming the spot swatch, the Swatches Palette does not show the spot actually used in the image. Changing the color values of the spot swatch before renaming changes the appearance of the image, but it does not after renaming. After saving and reopening the file, both the original spot(used in the image) and the renamed spot swatch will be visible in the Swatches Palette.

I've observed this behavior in the following installs:
MacOS 11.5.2, Illustrator versions 25.3.1 & 25.4.1
Windows 10, Illustrator version 25.2.1

It is important that the Swatches Palette correctly reports the spot colors used in images. The renaming of a spot swatch used in an image breaks at least one of the save scripts we use in production. It also causes an error upon saving on machines with Esko plug-ins installed.