For collaboration purposes, Is it possible to "Tag" a file that is being used or modified by another user in my group in order to prevent overwriting each others changes.  Basically letting others in the group know that a specific sheet or file that they are trying to access is being used or modified by someone else in the group at that time?  Any help or ideas would be greatly appreciated!   Thank you..

Well, unfortunately it is not possible to do so. Note HTTP connection is sessionless, i.e. when a request is processed, the connection is closed. When a user opened a file, before next action happens, the server doesn't know if the user is still using the file or not. So, if the server locks the file, and if the user has closed the browser (or FileManager), the file could be locked forever or until session times out.

FileManager will prompt for overwriting if a file is changed by another user. Please be careful to test this feature. A much better solution is to make sure that everybody copies the file to another folder and edit it. After done, copy it back to the shared folder.