I have identified the relevant threads and have read the pages in the
microsoft support website. Experts, please share with me:

full-proof.

A function IsFileOpen attempts to open a file for I/O. It then closes
it and returns TRUE if an error was produced while attempting to open.

Then, the attempt to open at Excel-level is done through invocation of
IsFileOpen in an IF.

In other words, broadly speaking, we have the following sequence of
events:

Open at I/O level.
Close at I/O level.
Workbook.Open

Thus, it is possible that between the Close and Workbook.Open someone
else has opened the file. Am I correct? Am I missing something?

Is there a full-proof way to open a file exclusively for write and then
use object libraries with it?

Regards,
Kostis Vezerides