find . -name "*.html" -print0 | xargs -0 perl -p -i -e 's|\Qhttp://66.36.242.244/~olxhxlwq/\E|http://www.johnclarkprose.com/|g'

find . -name "*.html" -print0 | xargs -0 perl -p -i -e 's|\Qhttp://66.36.242.244/~olxhxlwq/\E|\Qhttp://www.johnclarkprose.com/\E|g'

\Q...\E perl quoting means no ugly escaping in the regex. find's -print0 with xargs -0 is the secret to handling files with spaces in their names.

Perl Search and Replace One-liner with xargs -0

regex, Bash, replace, perl

Bash