Dear Mandar,
for changing status go to CNMASS to change status
or other way out is to access WBS element overview line items in CJ20N or CJ02 select all and go to Edit-->status-->Technically complete.
for not allowing user to carry out any postings or reversals just change status to AALK(account assignment locked)
for displaying WBS elements in the reports check with the dynamic selections and exclude the WBS elements whose status is techo or closed
Regards