Have you tried setting the file to be read only? In the command prompt the instruction would be: attrib +r "C:\folder\__Catalogue"
You can use os.chmod() function if you want to do it from within a Python script.
…but Revit is extremely annoying and limited when a file is read-only, it might be better to copy the file to a temporary location and open the temporary file.
It would be more reliable to have IT change the permissions to the directory that they reside in so that so only you (or a specific account type, ie. admin) can save changes to files in that directory. I know it’s not a very Revit thing to do, but it is very effective.
It is not to limit writing to a user, it’s to limit for REVIT version.
We ave many project in many REVIT version.
My goal is to make sure that no one converts a library from a given version to a higher version (making it unusable for REVIT from an earlier version)