sub change_ops
{
    my @ops = @_;
    my @newoptions = map { ++$. } ( 0 .. 3 );
    my $callback = $ops[0]->cget (-command);
    $ops[0]->configure( -command => undef );
    $ops[0]->configure( -options => \@newoptions );
    $ops[0]->configure( -command => $callback );
}