Blocking specific page cells in a pivot
 

Need to create pivottables from a cube where i just want to change one
parameter (user) before publishing a pivot. The User should be as page
selection and fixed. I have tried to block and protect but either it is not
possible to change the other page selections or it is possible to change
everything, including the user. I have found VBA code which could be used but
how do i get the code to run when I open the workbook? Is there an easier way?