How can I downgrade Safari 6 to 5 in Mountain Lion? [duplicate]
No, you can't go back with Safari on Mountain Lion.
Yes you can. See this answer:
How do you remove Safari 6 on Mac OS X 10.7.4
Sorry this answer is for downgrading Safari 6 in Lion only
Yes you can go back to Safari 5.1.7 from Safari 6. I found the uninstaller on this site. Third from the top is Safari 6 - Lion uninstaller, click this to download, run it, reboot and Safari 5.1.7 will (surprisingly) reappear, I have just done it, no problems though YMMV.