The Network Extender is managed from your computer using your My Verizon login.
From the FAQ page:
You can set your Network Extender for open or managed access. Open Access allows any Verizon Wireless phone within range to use your Network Extender. Under Managed Access, you have the ability to prioritize access to your Network Extender to up to 50 Verizon Wireless callers you select. Where a compatible cell tower is unavailable, callers that do not appear on your managed access list may access the Network Extender when not in use by priority callers. All callers may access the Network Extender for emergency (E911) calls.
Once you have your Network Extender hooked up, you will see a link for it in My Devices. Follow that link to switch from the default Open Access to Managed Access, then you can configure your Network Extender with your priority numbers.
Verizon makes it near impossible to find this link: http://support.verizonwireless.com/clc/faqs/Equipment/network_extender.html
Scroll down to the second section and click on the link they give telling you that you can add up to 50 names (bear in mind only 7? will work at any given time). I'd give that direct link, but for some reason it doesn't work. This is the best I can offer. What kills me is how the manual for the extender says if you have a blinking red system light, the extender is in an unstable condition. That's great help. Good luck!
I finally found the link to the instructions on how to add specific numbers to your priority access for the extender!!!
http://support.verizonwireless.com/support/devices/knowledge_base.html/21845/#add
You do NOT have to choose a device before following these instructions. The Network extender will be found on the right in its own section as the instructions state.