To change user group permissions without logout you will first need to remove all the users Kerberos tokens using the command below
This should show as below
Current LogonId is 0:0x7e3d67 Deleting all tickets: Ticket(s) purged!
To see the new list of Kerberos Tokens run the command below
To get a new Kerberos Token you will need to start a program as the user, the easiest way is to use runas and lauch a simple notepad window
runas /user:domain\username C:\Windows\system32\notepad.exe
To see the list of all the groups the user is now a member of run the command