restore() instead of snapshot() would bring u to the old state of your packrat library. Also packrat::on() might not be needed since you should be in packrat mode normally always when you are in a packrat project.
the suggestion seems to be the correct way to upgrade package in packrat lib.
Know also that packrat::packrat_lib() contains the path to the packrat private library. It can be useful.
If it is working for you, can you mark your question as solved
It will help other knows the status of the question right from the list of question or by searching for related topic.
Thank you.
I edited your post to add a more readable formatting