If you have full access into this router (ie you have access to toolbox. check note at the end if you don't), you can make address filtering using the firewall or parental control.
The easier way would be the parental control which I will write here:
Go to parental control in toolbox. Then configure.
Tick "Use Address Based Filter:"
Leave "Action for Unknown Sites:" as allow
Click apply
Reclick configure
Type the website or IP address that apple uses for software update (I couldn't find from a quick search on google) in Web Site.
Choose block
Leave Redirect as empty
Click add
Close the site and your done.
Note:
1)To access the router, type 192.168.1.254 (usually for this router) as a website. You might also need to use an ethernet for this router.
2)If you are using an Ogero, you need to contact Ogero at this email
chebaro@ogero.gov.lb and tell them you want the username and password for full access to the router (provide router type,phone number, line owner and Lnumber in the email). If you are using any other ISP, use (admin,admin), (user,user), or (adminstrator,
blank) usually (or contact them by phone or email).