Your problem seems to be a function of when, in Excel's boot order, commands are called.

use strict;
use warnings;
use Win32::OLE;
use Data::Dumper;

my $xl = Win32::OLE->new('Excel.Application');
$xl->{Visible} = 1;
#my $wb = $xl->Workbooks->Add;
print Dumper $xl->{Calculation};
$xl->{Calculation}=-4135;
print Dumper $xl->{Calculation};
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returns

X:\Data\Perl>1145425.pl
$VAR1 = bless( do{\(my $o = 40621128)}, 'Win32::OLE::Variant' );
$VAR1 = bless( do{\(my $o = 40621128)}, 'Win32::OLE::Variant' );
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But uncomment the line creating the workbook and you get

X:\Data\Perl>1145425.pl
$VAR1 = -4105;
$VAR1 = -4135;
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which is, I think, what you want.

Regards,

John Davies