I'm wondering if I have to do iisreset upon updating the urlscan.ini file. Is this required or will IIS pick up the new ini file immediately?
This depends on the version of UrlScan. The UrlScan reference site says:
UrlScan 3.0 added change notifications for the UrlScan.ini file, so it is no longer necessary to restart IIS after updating your UrlScan.ini file.
Hence, it does not require to restart IIS.