Portuguese guitar TAB

The easy way out might be to take the guitar tab template(s), modify their string data, save inder a different name in the personal templates folder and then use those when creating a new score.
1- If you modify the instruments.xml file, you'd need to add it in Preferences → Score too, otherwise just the builtin one gets used, (":/data/instruments.xml" is the built in one).
2 - That's why it might be easier to modify the string data of a template, there you can see D3, A3, etc. and don't need to know what MIDI pitch that equates to. You could than save the template as an mscx file, i.e. uncompressed and use a plain text editor on it to find the corresponding MIDI pitches.