You can edit EXIF with
ExifTool. It's command line, though there's a GUI version for Windows (not Mac). Once installed, you would enter:
ExifTool -model="My Camera" FILE
...where My Camera is Canon R5II or whatever you want to call it, and FILE is the RAW file/path. On the Mac in Terminal, you can just drag-and-drop the file into the Terminal window after the command.
However, that may not accomplish what you want. There is also a Canon Model ID field, and I'm not sure you can (or should) edit that. For example, I edited the Model of an R1 file, and in the full EXIF dump it shows the edited name for Camera Model Name. But Canon Model ID still shows Canon EOS R1, and that's what shows up in DxO as well. Like the LensID, the Model ID is an integer field that ExifTool and RAW editors (at least DxO) convert to a camera name. Looking a a few RAW files, the modelIDs are
- R1 = 2147484821
- R3 = 2147484752
- R8 = 2147484807
If you're set on this, dig into ExifTool, the documentation and forums have lots of information.
Note that I'm far from an expert here, but this is fresh in my mind since I
went through this yesterday and today for a lens + extender combo where I was trying to spoof DxO to use a specific module/profile. It turned out that the Lens Model and LensID were irrelevant for that, I just needed to change the focal length and aperture and DxO made the guess I wanted for the module to use.
The point is that the way different image editors parse the EXIF metadata is not straightforward. But...good luck!