how to write pl/sql named programme for this I have a table M_PARAMETER which has a column MMRUN.

When this MMRUN='Y' then the User can not modify any transaction in the app's front end. When MMRUN='N' then the User can do the modification.

emp,dept,salgrade table do not modify users when MMRUN='Y'
You could use a global system context to do this.  See here Oracle context

The user logs on, your stored procedure determines the value of MMRun for that user and the context is set for this session.
Then your triggers or insert/update/delete triggers or procedures refer to the context for permission to edit.

Really though this sounds like something that will require a more fine grained permission structure in the future. I've never seen something simple like can modify/cannot modify stay simple. Usually you are asked to provide variations on this in the future. There are  open source PL/SQL  packages available which can be adapted to do this.