When using the build and capture task sequence in MDT Lite Touch it make perfect sense to add date information to the WIM file name created. Since CustomSettings.ini understands inline VBScript you can simply set the following:
Update May 30, 2018: Formatted the code to use two digits in month and day.
BackupFile=%TaskSequenceID%_#year(date) & "-" & Right(String(2, "0") & Month(date), 2) & "-" & Right(String(2, "0") & Day(date), 2)#.wim
Note: Make sure you don't have " (curly quotes) in the .ini file but instead use " (straight quotes)
Sample
Below is the output from simulating (in PowerShell) a sample CustomSettings.ini file.
[Settings]
Priority=Init, Default
[Init]
TaskSequenceID=REFW10-X64-001
[Default]
BackupFile=%TaskSequenceID%_#year(date) & "-" & Right(String(2, "0") & Month(date), 2) & "-" & Right(String(2, "0") & Day(date), 2)#.wim

Happy Deployment, Johan