Show "Log in" link all the time (even for logged in users)
If you're trying to show a link called "My Shop" which takes anonymous users to the log in page and logged-in users somewhere else, you can just create a second menu item also called "My Shop" and set it to display only for users that have the authenticated user role.  Then set the destination to whatever you want; that way both logged in users and anonymous users will have "My Shop" links pointing different places.

You can have multiple menu items on the same menu with the same name (Drupal doesn't check for uniqueness in order to allow for situations like this).

As long as you give the two "My Shop" menu items the same weight (or drag them so that they are next to each other), they will appear to be the same menu item.