Thanks. What I read implied to me it would not be treated as the splat character unless it was at the beginning of the word; which might have been incorrect or because @ appears to have multiple uses that I did not see earlier. If the CLI_RESPONSE_PREFIX variable is set to something like underscore that might work but I the way it works now you have to change the @ to _ in the response file too. If I change that so the prefix just gets changed to @ so you do not have to change the files that might be useful.
So far a leading underscore looks safe but PowerShell appears to use a lot of special character sequences.
Oh well.