especially if its as distributed by a distro.
12.34.56.64-95 == 12.34.56.64/27
But... drop the period at the end of the regex and it should work.
IOW:
^12.34.56.(6[4-9]|[7-8][0-9]|9[0-5])$
This should work if you have rewrite on:
RewriteCond %{REMOTE_ADDR} 12.34.56.(6[4-9]|[7-8][0-9]|9[0-5])
RewriteRule . - [F]