If you want to temporarily change the PerlIO layers of a handle, your best bet might be to dup the handle.
use strict; use warnings; use PerlIO qw( ); sub dump_layers($*) { my ($prefix, $fh) = @_; my @layers = PerlIO::get_layers($fh); print($prefix, join(', ', @layers), "\n"); } dump_layers('before: ', STDERR); { open my $fh, '>&', STDERR or die $!; # Dup the handle binmode $fh, ':encoding(UTF-8)'; # Do anything to the dup. dump_layers('local: ', $fh); } dump_layers('after: ', STDERR); # The original is unaffected.
before: unix, perlio local: unix, perlio, encoding(utf-8-strict), utf8 after: unix, perlio

The package variable itself could be replaced with the dup for the duration of the inner scope, but it shouldn't normally be needed.