Download and install the full featured AirPort Utility 5.6 for Mac OS X Lion
Open up the application and click Manual Setup
Click the Internet icon
Click the DHCP tab under the icons
Edit out the DHCP Message and click Update to save the settings.
Might be a good idea to keep AirPort Utility 5.6 on your Mac along with 6.0....which you cannot delete.
is there another way?
If you have been using Time Machine, and had AirPort Utility 5.6 installed on Lion, go back in time before the "upgrade" to Mountain Lion and restore AirPort Utility 5.6 to the desktop.
Then, simply move it into the the Utilities folder in Mountain Lion and it will co-exist with AirPort Utility 6.1.
Works fine for me....but since this is not officially supported....there are no guarantees.
With my new Macbook Pro (Retina), I'm having this issue badly. Repeatedly displays the custom "Welcome" message I entered in years ago. Doesn't show up on the other Macs on the network (iMac 2011 and Macbook Pro 2007) or any of the iOS devices. As mentioned in another post, the Airport Utility 5.6 is unable to be installed on Mountain Lion. Anyone have another suggestion?
the Airport Utility 5.6 is unable to be installed on Mountain Lion.
See this article to learn how to install AirPort Utility 5.6 on Mountain Lion:
Can't Turn off on Welcome message for AIRPORT or TIME CAPSULE solved
This is a fairly simple process to do, and it works with any version of AIRPORT utility.
Step 1: Open AIRPORT Utility
Step 2: Click the EDIT button on the AIRPORT/TIME CAPSULE you want to modify or delete the Welcome message
Step 3: From the FILE menu, choose Export Configuration File. Note the name of the file you exported.
Step 4: Open FINDER and find the file name you exported. Using TextEdit program, open the file you exported
Step 5: Do a find on the string dhMg
Step 6: You will see a string such as:
<string>Welcome to my wireless network or this might be blank</string>
Step 7: After the <string> Enter any message you want or delete a message if you no longer desire. It will look something like
<string>Welcome to the UXO.NET Wireless Network.</string>
or if you want to delete messages
Step 8: Save the TextEdit file
Step 9: From the AIRPORT utility, choose IMPORT CONFIGURATION FILE
Step 10: Select the file you just saved
Step 11: Click UPDATE button. AIRPORT/TIME CAPSULE will reboot
Step 12: Enjoy your new message or lack thereof