You should be able to use CIDR notation in order to allow subnets:
Allow from 10.1.0.0/16
If you have a large or more specific range to block or allow, it might be better to consider blocking in the firewall directly, as having too many allow/deny rules in htaccess or your Apache configuration might slow down your page serving by a considerable amount since all of these items will be parsed on each and every request.
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