Turn ON Custom Error and disable debug mode

Aloha,
We have a ASP .Net based web service setup and hosted on a IIS v6.0. We wish to turn on custom error and disable debug mode. I understand these can be accomplished by modifying the web.config and machine.config file. However, since web service does not have a UI...please let me know if the changes made to the config files will take into effect. The reason why we wish to do these changes is because, our external auditors have flagged these as a vulnerabiity.
 
Thanks,
Venkatesh Selvaraju
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