There is no warning message when replace.py is not able to save a page because blocked by the spam filter.
For example try to run this on en.wiki:
replace.py "http:// www." "http://www." -page:"Mercedes-Benz S-Class (W220)"
Version:
Pywikibot: [https] r-pywikibot-core.git (6a84859, g7382, 2016/08/06, 00:29:37, n/a) Release version: 3.0-dev requests version: 2.11.0 cacerts: C:\pypy2\site-packages\requests\cacert.pem certificate test: ok Python: 2.7.10 (91db1a9b7bfd, Aug 15 2016, 02:47:11) [PyPy 5.3.2-alpha0 with MSC v.1500 32 bit]