Windows – Permanently add a firewall exception on Windows 7

As stated by Joe Internet in the comments, you can specify the Service you want to use. For that, you have to define a new outbound rule, but use "Custom" instead of "Program". There, you can choose the service, in your case "Windows Update", or also "wuauserv", which should be exactly what you're looking for.

According to the Windows Firewall documentation, block rules always take precedence over allow rules, therefore even if your allow rule looks more specific than a block rule, the allow rule will not work, and the traffic matching both allow and block rules will be blocked. The option “Allow this firewall rule to override block rules” is available only for rules which require IPSec, and is not available for outbound rules.

The only thing you could do with Windows Firewall to achieve something close to what you need is to switch the default behavior for outbound connections to “Block”, then add explicit allow rules for all outbound connections that you need (not just for that single program). Alternatively, you can look for third-party firewall software with more features.