This is difficult to do.
- There is no API support for even finding protected questions, much less (un)protecting posts.
Even a web-bot couldn't do it all, as there is no way for low rep users to search, manually, for protected posts.
**Update: ** As Catija reminded, there is a tools/protected-questions page for 10K users.
SEDE can find protected questions, but is difficult to automate and the data is up to a week old. And, If you automate the SEDE query via Google’s BigQuery, the data is only updated quarterly.
So, currently(API version 2.2), you would need to write a hybrid app, and/or a userscript, that:
- Finds protected posts by web-scraping SEDE or the protected-questions page.
As a logged-in user, web scrapes the actual site to navigate to the posts, possibly verify that they haven't changed, and unprotect them as desired.
(Note that the userscript would automatically be logged in by running in browser tab(s) where the high-rep user already had a session established.)