Can you explain more your requirements?
Because I'm sure that this won't work for you.
SELECT inputString, SUBSTRING( inputString, 1,42) + SUBSTRING( inputString, 105,16)
FROM (SELECT 'BUILTIN\ADMINISTRATORS: [System Admin]YES;[Security Admin];[Server Admin];[setup Admin];[Process Admin];[Disk Admin]YES;[Database Creator]' AS inputString) Input
However, it gives the correct output.