It's a big ugly, but you can use select and $~ to change the format for a given filehandle. See perlform for more info. In the meantime, here is a brief example:

use strict;
use warnings;

open( my $outfh, '>', 'temp.txt' ) or die $!;

my ( $var1, $var2 ) = ( 'one', 'two' );

my $oldfilehandle = select $outfh;
$~ = "FORMAT1";
select $oldfilehandle;
write $outfh;

$oldfilehandle = select $outfh;
$~ = "FORMAT2";
select $oldfilehandle;
write $outfh;

$oldfilehandle = select $outfh;
$~ = "FORMAT1";
select $oldfilehandle;
write $outfh;


format FORMAT1 =
    @<<<<<   @<<<<<
    $var1,   $var2
.

format FORMAT2 =
    @<<<<<XXX@<<<<<
    $var2,   $var1
.

close $outfh;
[download]

    one      two
    two   XXXone
    one      two
[download]