Sure. You just need to turn the wireless radio off in the router's configuration webpage. If Verizon didn't give you documentation on how to do this, you'll need to contact them for details. Just let them know that you want to disable the wireless functionality in their router as you intend to use your own.
As cwa107 mentioned, contact Verizon. However, some info you need to know about FIOS: The router provided by Verizon is more than just a "router". It also interacts with your TV (s) to their system so that it can receive messages and at the same time, the on screen guide. Additionally, if it's removed, you will also lose Pay Per View.
You'll need to keep the Actiontec in the circuit while at the same time bypassing it and using your Time Capsule just for wireless. Make sure when you call Verizon support, you get someone who is familiar with Mac machines and OS X.
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