The best way to format all text in a Excel workbook is to change the Normal Style setting. Here is an example:

    #!/usr/bin/perl -w


    use strict;
    use Cwd;
    use Win32::OLE;
    use Win32::OLE::Const 'Microsoft Excel';


    my $application = Win32::OLE->new("Excel.Application");
    my $workbook    = $application->Workbooks->Add;
    my $worksheet   = $workbook->Worksheets(1);


    $workbook->Styles("Normal")->{Font}->{Size} = 8;
    $workbook->Styles("Normal")->{Font}->{Bold} = 1;


    # Write some text.
    $worksheet->Cells(1,1)->{Value} = "Hello World";


    my $dir = cwd();

    $workbook->SaveAs({FileName   => $dir . '/win32ole.xls'});
    $workbook->Close;


    __END__
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Note that this is applied to all worksheets in the workbook.

--
John.