If all you're doing is printing the result, you don't need variables at all:

#!/usr/bin/env perl

use strict;
use Date::Calc qw(:all);

printf "%d%.2d%.2d\n", Add_Delta_Days( Today(), -1 );

__END__
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But if you want to keep those three values around as properly formatted separate strings, you could do it this way:

use strict;
use Date::Calc qw(:all);

my ( $year, $month, $day ) = map { sprintf "%.2d", $_ }
    Add_Delta_Days( Today(), -1 );

print join '', $year, $month, $day, "\n";

__END__
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