Rated 5 out of 5 stars

How can I change the shorcut? (open new private tab?)

This review is for a previous version of the add-on (0.1.7.5.1-signed). 

You can modify extensions.privateTab.key.openNewPrivateTab preference in about:config, see
https://github.com/Infocatcher/Private_Tab/blob/0.1.7.5/defaults/preferences/prefs.js#L9-L16