Automatically name computers using existing computer name

Question

In my environment, I have brand new computers to be imaged.  The computer name needs to consist of the room number and the serial number.
I am utilizing the Collection Variables within All Unknown Computers collection to define the room number.  And I am using CustomSettings.ini to automatically grab the serial number and combining that to the room number to OSDComputerName.
That is working perfectly fine.
My question is how to automatically use existing computer name as the name of the re-imaged computer?
If I use the same task sequence, because the computer is no longer an unknown computer, it doesn't prompt me for the room number.  The computer name ended up containing the variable %roomnum% plus the serial number.  I do not want SCCM to prompt
me for anything but automatically use the existing computer name.
Please advise.

Answer 1

Maybe I am missing a step.
This is my current CustomSettings.ini file
[Settings]
Priority=Init, Default
Properties=ComputerSerialNumber
[Init]
ComputerSerialNumber=#Left("%SerialNumber%",7)#
[Default]
OSDComputerName=%RoomNumber%%ComputerSerialNumber%
OSInstall=Y
SkipCapture=YES
SkipAdminPassword=NO
The variable %RoomNum% is defined in the All Unknown Computer collection and a prompt appears for me to manually enter that information before imaging the computer the first time.
But when I reimage an existing computer, I get no prompt and because the variable is not defined, the final computer name because %RoomNumber%9999999, which is longer than 15 characters and so the task sequence fails.
How and where in the task sequence do I define: if this is not an unknown computer, then use existing computername?
I also notice that I can add a step called "Capture Windows Settings-Migrate Computer Name".  Is this the step that I need?  Where in the task sequence should it be added to?
Here is a section of my task sequence. I didn't change much from the default created MDT Task Sequence.