How to control %_SB

Hi
I try to make an install that is supposed to work either on a Terminal
Server or local installation, but with slightly different folder names
and some ini settings.
So, I make this, where I try to change the %_SB_INSTALLDIR%.
This works when just going forward, I get default install folder set,
but when the dialog #3 (select install folder) has been displayed, it
takes total control of the variable %_SB_INSTALLDIR% and I can't change
it again. If I remove the Select Install Folder dialog, I can go back
and forth as I want, but then I won't be able to override the install
location, which I think is good UX.
Suggestions?

[ User Interface ]
! Wizard dialog definition(s)
Define Wizard Dialog "WELCOME" (Welcome) -- Install startup program
and/or barcode fonts
Define Wizard Dialog "SELECTINSTALL" (Radio Buttons) (%INSTALLTYPE%)
Define Wizard Dialog "#3" (Select Install Folder) (%_SB_INSTALLDIR%)
Define Wizard Dialog "READY" (Ready to Install) ()

! The Wizard Loop displays the dialog screens that the user sees in the
installation
Loop Wizard (Abort Dialog Active)
If %_SB_DIALOGID% Equals "$SELECTINSTALL$" Then
Set Variable %USERNAME% to FUNCTION:Get System Info (User Name)
If %INSTALLTYPE% Equals "1" Then
Set Feature State (NotSelected: "Local")
Set Feature State (NotSelected: "Barcodes")
Set Feature State (Selected: "Terminalserver")
Set Variable %_SB_INSTALLDIR% to "D:\SvenheimLT\%USERNAME%"
Else
Set Feature State (Selected: "Local")
Set Feature State (Selected: "Barcodes")
Set Feature State (NotSelected: "Terminalserver")
Set Variable %_SB_INSTALLDIR% to "C:\AdiFakt"
End
End
End

Bjarne Havnen

How to control %_SB_INSTALLDIR%