import re
s= ' Get exciting offers when you book a XX year car June XX - XXXX Click here to book http://a...content-available-to-author-only...c.in/XXzOK '
s = re.sub(r"(https?://[^/\s]+/)(\S+)", lambda x: x.group(1) + 'X' * len(x.group(2)), s)
print(s)
aW1wb3J0IHJlCgpzPSAnIEdldCBleGNpdGluZyBvZmZlcnMgd2hlbiB5b3UgYm9vayBhIFhYIHllYXIgY2FyICAgSnVuZSBYWCAtIFhYWFggQ2xpY2sgaGVyZSB0byBib29rIGh0dHA6Ly9hLi4uY29udGVudC1hdmFpbGFibGUtdG8tYXV0aG9yLW9ubHkuLi5jLmluL1hYek9LICcKcyA9IHJlLnN1YihyIihodHRwcz86Ly9bXi9cc10rLykoXFMrKSIsIGxhbWJkYSB4OiB4Lmdyb3VwKDEpICsgJ1gnICogbGVuKHguZ3JvdXAoMikpLCBzKQoKcHJpbnQocyk=