You can change the user. If you use your connect to server method (see IIP avPrivateConnect) you can make the user connect as one user profile and return another. Or you can modify IIP avSetSessionValues to give a user a different session value for user profile.
Or in client server applications, you can change the user that is shown by changing the value of field CHK_VUSER in the RDML of the Server IIP function to validate sign on (default is function UFU0005). See the source code of UF_SYSBR/UFU0005 for more details.
The user profile and password are validated by your custom version of UF_OLOGON.
Refer to the shipped example's comments related to parameter UserNameToDisplay.