I have configured mod_jk to allow load balance. I want to know if more workers could be dynamically added to workers.properties while apache is running?
No. workers.properties file is configured in some .conf files, to make change to .conf file take effect, you need to restart Apache.
See the thread about mod_jk configuration: http://milestonenext.blogspot.de/2012/09/ssl-offloading-with-modjk-part-1.html