It depends on your definition of "easy". Here's how to do it.
You have to do the renames one file at a time and from with in RM. Go into Lists>Media Gallery and highlight the file you wish to rename. This can be easier said than done. I find it easiest to do if I first click the List button down in the lower left hand corner of the Media Gallery sub-window so I can see the file names. RM doesn't remember this setting, so I often have to repeat this step. It's further easiest to do if I next enter a portion of the existing file name into the search box in the upper left hand corner of the Media Gallery sub-window and click the Search icon (the looking glass icon). This filters the list of files to only those files containing my search string. Then I highlight the file I wish to rename.
Having done so, I click the Properties button and the Change Media File button. RM does not think I'm going to rename the file. RM thinks I'm going to replace the existing file with a different file. So we will just leave RM in total ignorance of what we are really doing.
The Change Media File button places you into a Windows File Explorer sub-window from which you can select a "different" file from the one you are currently using. You need to select (click on) the existing file (not a "different" file), click press F2 to go into the Windows File Explorer dialog to rename the file, then rename the file, select the renamed file, and click Ok. RM will think it has replaced the "previous" file with a "different" file. What has really happened is that the file with the "previous" name has been replaced by the same file with a "new" name.
This process is somewhat cumbersome, but it's much easier than any of the alternatives I've been able to come up with. And it's extremely safe in the sense that if your file has been tagged many, many different place in RM then all those tags will be preserved.
I use a similar process if I really do wish to change to a different file. For example, I might have RM linked to a PDF file and I decide to extract the image from the PDF file into a JPG or PNG file instead. The same process can be used to redirect RM to the JPG or PNG file without losing all the existing media tags in RM. The existing media tags are the things that are difficult to replicate if they are lost.
Back to the rename process in Windows File Explorer: if there are many, many files in the folder in which you are working, it can again be difficult to find the specific file you seek to rename. I find it very helpful to change the view in Windows File Explorer from the default of large thumbnail to Details view or List view. You really need to see the file name, not the picture.