How to change the default VNC client

remote desktop

I have a VNC Viewer installed. Is it possible to make it the default VNC client?

I would like to get rid of the built-in Screen Sharing app and automatically open VNC Viewer whenever I type

open vnc://server:port

in Terminal.

Try the RCDefaultApp preference pane at http://www.rubicode.com/Software/RCDefaultApp/. It lets you choose the application to be launched for all sorts of situations.

Install it, open it (it becomes the "Default Apps" preference pane), and then choose the "URLs" tab:

Scroll down to the "vnc" prefix, and then choose what you like from the "Default Application" popup.

On OS X Yosemite the Screen Sharing app moved to the applications subfolder:

/System/Library/CoreServices/Applications

The questioner already has a .vncloc file, so the simplest answer is to add the username into that file:

Locate the file. (If you haven't moved it, it'll probably be in ~/Library/Application Support/Screen Sharing/.)
Ensure you have write permission. (E.g. with the Finder, or chmod +w.)
Open it in your favourite text editor (e.g. vim).
Edit the first line with vnc://<address> to read vnc://<username>@<address>.
Save it.

The file will then connect directly to the remote system, skipping the password dialog entirely.

You can run it by double-clicking on the file in the Finder, dragging the file onto the Dock, or using open from the command line.

(Alternatively, you can include the username in the vnc: address when first creating the file.)