I think you can change it with multi beast, but I was uncertain how to avoid changing anything else, so I just edit the text file where the information is stored.
If you can edit a text file, you can fix it.
First use a code editor (not MS Word or similar). For things like this Text Edit will work fine, so long as it saves in plain text mode.
The information is in a file at /Extra/smbios.plist. Open the system drive at the root where you will find the /Extra folder. Open it an drag the smbios.plist to Text Edit.
If for some reason Text Edit will not cooperate you can use the terminal:
sudo nano /Extra/smbios.plist
Which will launch a simple editor (<control>O<return><control>X to save and exit after making your changes.
If that proves daunting, you can try:
sudo open /Extra/smbios.plist
Which will bring it up in whatever editor Mac OS X thinks appropriate for plists. (a very nice one if you have Xcode tools installed)
All three work for me, so you should be able to find a way.
Here is the first part of that file with appropriate values in it:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>SMfamily</key>
<string>iMac</string>
<key>SMproductname</key>
<string>iMac14,2</string>
<key>SMboardproduct</key>
<string>Mac-27ADBB7B4CEE8E61</string>
You will notice the SMFamily is iMac, the SMproductname is iMac14,2 and SMboardproduct is Mac-27ADBB7B4CEE8E61.
The first two should be changed, the third item, was changed in the Multi beast output, so it should probably change also.
Save the text file. If it is a fusion drive or appleraid drive, copy the /Extra folder from the main drive to each of the Boot OS X partitions, as you were instructed in setup guide.
The change will take full effect after a restart. Look in About this Mac and System Profiler (More Info... -> System report).
