Is there any metadata that can't be changed in a cr2 and nef files?

[AL10]

I'm a bit new with learning about the ExifTool, so I apologize for perhaps asking a very simple question. Here is my concern/question:

Are there any certain parts/variables of metadata that the tool cannot change? My concerns are particularly for .cr2 and .nef files.

I ask this because I need to know that I'm receiving original photos from my clients. This is why for my purposes, I'm only asking for .cr2 and .nef file formats since they cannot be saved over with out the addition of an xmp file and both these file formats can be converted to their original state using both canon and nikon software. HOWEVER, after reading up on the ExifTool I see that it is capable of changing metadata with both these file types, so my concern is that I will never know if I am reading the original metadata from a photo or if it has been changed using a tool like ExifTool. This is why I asked if there is any specific metadata that the tool cant change so I know at least one variable of the photo is correct.

[StarGeek]

You can take a look at the various Canon, CanonCustom, Nikon, and NikonCustom tags that exiftool can decode and focus on one that's listed as one it can't write to.  Or use

But that doesn't guarantee that some other software can't edit those entries or even the possibility of someone editing the data by hand with a hex editor.

Metadata cannot be write-protected.

[AL10]

Thank you for the reply