What's the server side process for .dhtml files? Are they generated via perl cgi script? If so, what's wrong with params? /viewquestions.dhtml?action=adminmode"
Then the question moves to when constructing the link, whether or not you need add the params. That can be solved tons of ways but normally you have some type of session associated and within that session there is something that identifies the user as an admin or not. If the user is admin, construct the link with the param, else construct the link without it.