You can prevent the callback from being triggered by setting the variable to the first item of @newoptions before changing the options.

sub change_ops
{
    my $op = shift;
    my $var = $op->cget('-textvariable');
    my @newoptions = map { ++$. } ( 0 .. 3 );
    my ($prev) = (grep {$_ eq $$var} @newoptions) || '';
    $$var = $newoptions[0];
    $op->configure( -options => \@newoptions );
    $$var = $prev;
}
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