Table: user( name, last_name, age, ..., sync_status )
IF (TG_OP = 'UPDATE' ) then

     if new.sync_status != syncstatus_pending then
        if old.sync_status = syncstatus_pending and new.sync_status != old.sync_status then
           raise notice 'Sync status updated, It means we are changing from sync pending to sync yes';
           return new ;
        else
           raise Exception 'The synchronization status is not configured correctly.' ;
        end if ;
    end if;
    -- Check if we are trying to update a not synchronized row
    if old.sync_status != syncstatus_yes then
       raise Exception 'It was not possible to update rows are not synchronized.';
    end if ;
    if new.name = old.name and new.last_name = old.last_name and new.age = old.age
    and old.sync_status= syncstatus_yes and new.sync_status= syncstatus_pending then
   -- all columns are the same except the sync one, it means that we require sync this row but not to add to log_table
    return new;
   else
   -- process to insert in the other 'log' table
   -- ...
    insert into log_table ( )
   end if ;
end if ;