use strict;
use warnings;

my @lines = (
   "Once upon a time",
   "scrooge & donald",
   "went for a long walk"
);

my $lines = join("\n", @lines) ."\n\n";

my @list = ("huey", "dewey", "louis");

foreach my $who (@list) 
{
   my $new_lines = $lines;
   $new_lines =~ s/(&\s*donald)/& $who/;
   print $new_lines;
}

__END__
Once upon a time
scrooge & huey
went for a long walk

Once upon a time
scrooge & dewey
went for a long walk

Once upon a time
scrooge & louis
went for a long walk