To prevent editing cells in the data table, use Set Edit Lock with the Modify Cells argument.
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
dt << Set Edit Lock( "Modify Cells" );
dt << Set Edit Lock( "Add Columns", "Delete Dolumns");
dt << Set Edit Lock( "Add Rows", "Delete Rows");
dt << Get Edit Lock();
{"Modify Cells", "Add Rows", "Delete Rows", "Add Columns", "Delete Columns"}
dt << Clear Edit Lock( "Modify Cells" );
dt << Lock Data Table( 1 );

Help created on 10/11/2018