Copy to Instance
Very simple - this just scans selected objects and converts them into instances of the pre-selected master object. For when you make lots of copies of something then realise they should have been instances... Will scan objects to ensure they are of the same class before conversion (so if you have a light as the Master object - it won't instance any meshes - etc)
Installation Instructions:
Standard Maxsripts (.ms) can be run from the Maxscript button in the utilities panel. To have them always available - save the scripts into your scripts/startup directory.
Macroscripts (.mcr) can be placed in either scripts/startup or UI/Macroscripts - and are then accessed through the 'Customise User Interface' menu in 3dsmax. You can then assign the script to a keystroke - or a button. All macroscripts will appear under the 'Dusk' category in the dropdown.