create a new part with template (either mmns or ftlbs) as proe defaults. Now make changes as you wish. For example add density, material, drawing parameters etc.
Now save a copy of this start part. Go to your default working directory where your this start part you saved. Right click and rename this part. Delete the extension (.1) from your part xxx.prt.1, click ok when asked to change file type.
Now copy this part file instead of proe versioned file and save it in the Templates folder of ProE installed location.
Now exit proe and restart, uncheck default template and there you will see your new start part template.
The same rule applies to drawing template and assembly template.