Refreshing user's group membership in active directory without log-off/log-on

No supported way that I know of. You MAY be able to use RUNAS to start a command prompt with a new session and specify your same account name again... and that may do it... but I'd be running most (if not all) things that need special permissions as services and/or under service accounts.

• Open Task Manager
• Kill all instances of explorer.exe
• Go to File → "New Task (Run...)"
• Type in cmd
• In the command prompt type RunAs /user:<domain>\<user> explorer.exe

Done.

Is Gpupdate something that would work for you?

http://technet.microsoft.com/en-us/library/bb490983.aspx

Refreshes local and Active Directory-based Group Policy settings, including security settings.

gpupdate [/target:{computer|user}] [/force] [/wait:value] [/logoff] [/boot]