No. But you could do that after reading the YAML file, using s///. Something like this:

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my $hashref={
    ABC => 123,
    PATH => '$ENV{PATH}'
};


print Dumper($hashref);

s/\$ENV{(.+?)}/$ENV{$1}/g for values %$hashref;

print Dumper($hashref);
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Alexander