I tried to figure out how to always open any file in Notepad as Administrator via the Explorer shell menu, and with some help from this forum, I have succeeded!
1. Enable the Built-in Administrator Account
2. Set the password on the Administrator account to, say, "YOUR_PASSWORD".
3. Run regedit.
4. Goto to HKEY_CLASSES_ROOT\*\shell\
5. Create a new key named "Open with Notepad (as Administrator)"
6. Select the new key, and create another named "command".
7. Right click on the value named "(Default)" and select "Modify...".
8. Set the value to "runas /savecred /user:HOSTNAME\Administrator "notepad %1"".
a. Ensure that you leave quotes around "notepad %1".
b. Ensure that HOSTNAME matches the name of your machine.
9. Right click on a text file, and select "Open with Notepad (as Administrator)" from the shell menu. You'll be prompted for the password that you provided in step 2. You will only be prompted for this password once (due to /savecred).
You might want to combine this tip with "Image File Execution Options" to replace the built-in notepad with a better one (like Notepad2
One annoying downside of this method is that even after you provide the password, a command prompt briefly flashes before opening notepad. I'm not sure how to prevent this.
Also, I'm not sure if you'll have to reenter the Administrator password after rebooting or otherwise logging out (haven't tested that yet).