Make the part/template as you wish and save it as a (*.prtdot). Add the file location in
Tools (menu) - Options - System Options - File Locations - Document Templates
Or save it where the default templates are stored
Ingvar Magnusson may I add....
Alfredo Villasenor After you create your custom part template or any other changes to your settings do the following to eliminate a lot of frustrations later by saving your settings as well, one the the Tools/Options/Document Properties save the Drafting Standard to external file
Another good habit is to create a SEPARATE folder (outsides of the SolidWorks default folders) to keep all your custom templates, etc.
I use C:\SolidWorks Customization\SW20yy\Custom aaaaaa .
I have the last 4 releases installed, thus the SWyy sub-folder.
Then create a sub-folder ("Custom aaaaa") for anything you are customizing (to match the default SW folder structure).
This is a good place for your customized toolbox.
Now, at upgrade time, all your custom files stay untouched by the SW Installer.
Then restore your settings (as per John Stoltzfus) and you are back in business.