Is there a setting to keep the "Detail No." specific to the assembly where this screw appears? This screw could appear in multiple assemblies and multiple job numbers, my company assigns job specific detail numbers to metric screws. When I insert the screw from the toolbox and change the detail number to the new job it changes all previous detail numbers to the new job detail number.
It's been quite a while since I used Toolbox, but in order to accomplish that I believe you'd have to save out the Toolbox part as a separate, distinct file each time it's used in an Assembly. And if you do that be sure to remove the Toolbox designation or de-select the option that will look for Toolbox parts in the default location (see #5 at Frequently Asked Forum Questions) .