Easiest way to do all this with Sashimi:
1) Download PHM Regedit (it's free)
2) Make the registry edit you want to make in your registry
3) Navigate to the reg entry you just made in PHM and then tap and hold on the folder containing the entry and hit 'Export'
4) Name the .reg file whatever you want, but make sure you select 'Regedit 5' as the output 'Type'. Save the file wherever
5) Take the reg file you just saved and place it in the Sashimi\Auto\REG folder
That's it. Now when you run Sashimi, it will automatically install the registry entry for you