Mark everything shared with guest account as unwatched.

mark_guest_unwatched.py

# encoding=utf8
import sys
reload(sys)
sys.setdefaultencoding('utf8') #encoding incase item title has non ascii characters

from plexapi.server import PlexServer
from plexapi.server import CONFIG
import requests

# Edit these
PLEX_URL = ''
PLEX_TOKEN = ''

if not PLEX_URL:
    PLEX_URL = CONFIG.data['auth'].get('server_baseurl')
if not PLEX_TOKEN:
    PLEX_TOKEN = CONFIG.data['auth'].get('server_token')
# 

sess = requests.Session()
sess.verify = False
plex = PlexServer(PLEX_URL, PLEX_TOKEN, session=sess)

guest = plex.myPlexAccount().user("Guest")
token = guest.get_token(plex.machineIdentifier)
guest_plex = PlexServer(PLEX_URL, token, session=sess)
guest_sections = guest_plex.library.sections()

for section in guest_sections:
    if not section.title == "Music": #Skip Music library
        print("Marking section: {} unwatched.".format(section.title))
        for items in section.search(unwatched=False): #only check files not unwatched
            print("Marking item: {} unwatched.".format(items.title))
            items.markUnwatched()

Uses config file if PLEX_URL and/or PLEX_TOKEN are not filled out. Skips Music library as those fail when marking unwatched. Encoding is UTF-8 as to handle special characters in file names better.