You cannot easily alter the utilities within Lighthouse Studio's Choice Simulator. But, the same market simulator is available as a standalone software package and has the same functionality and UI. If you're licensed for Lighthouse Studio, then you (and your clients) are also covered for using the standalone Choice Simulator. Here's where you download it:
I have found myself manipulating utility files and reading the manipulated file into Sawtooth Software simulators for over 20 years now. The key file you'll be manipulating is the .HBU file. It's a space-delimited text file you can manipulate with a text editor and/or with Excel.
My favorite way to work with an .HBU file is to open in Notepad and take the global header rows out (move them into a text file for holding purposes). Then, open the remainder of the file (the rows of respondent data; one row per respondent) in Excel; modify the utilities in Excel, and save them out to a space-delimited text file.
Then, I take the global header and put it at the top of the modified respondent records and save it as a new and modified .HBU file.
Then, open that .HBU file using Sawtooth Software's standalone Choice Simulator software.