with open("index.html", "r", encoding="utf-8") as f:
    html = f.read()

import re
html = re.sub(r'<script\s+src="app\.js[^"]*"></script>', '<script src="app.js?v=1003"></script>', html)

with open("index.html", "w", encoding="utf-8") as f:
    f.write(html)