No, a user cannot add a new application that has not already been allocated to their list during signon.
You can think of USERMENU as a HIDE/SHOW function. This does not allow a user to dynamically add new applications to their menu. USERMENU manipulates the user resultant applications (session list) that they get from the sign-on process to Teleview.
If a user has the DYNAMIC application on their menu, then they select DYNAMIC and route to any accessible application provided they specify the APPLID.
A user session list can come from a profile or even be generated by the global security exit base security call (user coded VSON, if used). In addition, if a new application is added to the resultant session list and the user has already used USERMENU to modify their menu, then the new application will not appear until the user adds it to his active list with USERMENU.
There are many ways to get the session list. The user may be pointed to a default profile or a group or department profile or dynamically generated by security calls (VSON or VSLX exit). In general, the Teleview administrator can add an application to a profile that user points to, like by INSTDATA. If they implement dynamic session in VSON, then the security administrator would create some entry to USER.
The above assumes dynamic users. For static users the administrator would update the user to have applications in their user session list or a profile that the user is assigned. In addition, a static user can be pointed to a user list that has a profile plus individual applications.