Try an experiment - make a web service that writes USERID into a table. It will be your user ID, not the user ID of the account running the NAV service.
I should say - when you call the web services, it will be your local account if the calling code has a line like this
ws.UseDefaultCredentials=true;
otherwise, it will be the credentials specified by the calling application
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Its not possible to make the ServiceUser switching dynamically, I dont even see a reason why you would even want this.
Try an experiment - make a web service that writes USERID into a table. It will be your user ID, not the user ID of the account running the NAV service.
I should say - when you call the web services, it will be your local account if the calling code has a line like this
ws.UseDefaultCredentials=true;
otherwise, it will be the credentials specified by the calling application