Hope to move this to a dedicated script repo soon! But for backups sake:

date-recursive.py

from glob import glob
from pathlib import Path
from sys import argv
from os import system
from re import search, RegexFlag
from datetime import datetime
#exiftool -r "-FileCreateDate<DateTimeOriginal" "-FileModifyDate<FileCreateDate" "%1%"

DATE_FORMAT_STRING = "%Y%m%d_%H%M%S__"  # == yyyyMMdd_HHmmss__
NAME_FORMATTED = r"[^a-z]{1,}_{2}"
MODES = ["prepend", "undo"]
DIRECTORY = "D:/Pictures/**/*"

args = [arg.lower() for arg in argv]

apply = "--apply" in args



def prepend(filename):
    path = Path(filename).absolute() 
    if path.name.startswith("IMG_"):

        # st_mtime is last modified
        file_date = datetime.fromtimestamp(path.stat().st_mtime)

        new_path = path.with_name(file_date.strftime(DATE_FORMAT_STRING) + path.name)
        print(f"""

            Renaming:
                    {path}
                --> {new_path}
            """)
        
        if apply:
            # I think this was for some iphone weird stuff
            system(f'exiftool -r "-FileCreateDate<DateTimeOriginal" "-FileModifyDate<FileCreateDate" "{path}"')
            path.rename(new_path)


    else:
        print(f"NOT processing {path.name}")

def undo(filename):
    path = Path(filename).absolute()
    should_be_undo_ed = search(NAME_FORMATTED, path.name, RegexFlag.IGNORECASE)
    if should_be_undo_ed is not None:
        to_remove = should_be_undo_ed.group(0)
        new_path = path.with_name(path.name.replace(to_remove, ""))

        print(f"""

            Renaming:
                    {path}
                --> {new_path}
            """)
        if apply:
            path.rename(new_path)

    else:
        print(f"SKIPPING {path.name}")

        

print(
    f"""
    This script can:
        {MODES[0]}: prepend {DATE_FORMAT_STRING} to files
        {MODES[1]}: remove that prepend
    """)


mode = input("Select mode: ").lower().strip()

if mode not in MODES:
    exit(0)

# Prepend
if mode == MODES[0]:
    handle_file = prepend
# Undo prepend
elif mode == MODES[1]:
    handle_file = undo


files = glob(DIRECTORY, recursive=True)
for file in files:
    handle_file(file)