Here is the summary for this issue. Christos Katsis from PTC helped a lot. Thanks Chris
[...] *After you create a shell property and you save it in a library, the library file will appear in your home directory. On a windows machine, that's C:User Profiles\username by default. I have attached one such file for your reference.* [...]
I didn't pay attention to Mechanica's Help file 😞 : [...] *The default location for all library files is your home directory, but you can move it to a different directory, You can use the environment variable $HOMEDRIVE$ to set your home directory on Windows platforms.
When you access the library, Mechanica looks for the library file in the following directories in this order: 1) The directory from which you started Mechanica 2) Home directory () 3) the lib subdirectory of the Mechanica Home Directory You can move or copy the library files into any of the above directories* [...]
here is the mechanica_shell_properties_library file *mshlprp.lib*