Unless I misunderstand what you're asking for; you can do the assignment multiple times with different values:

$text = sub {
<<EOT;
Dear $person,
I know that this text is $adjective.
But I wish it could be...
EOT
};

my @subs=('Mom:not interpolates',
        'Dad:maybe interpolated',
        'Sis:who knows');
foreach (@subs){
  local ($person,$adjevtive)=split ':',$_;

  print &$text;
}
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My technique will also work for your number example (with everything stored as a function). However it look slightly ugly:

$n = sub {1};
$m = sub {&$n*2};
$o = sub {&$m*2};
$s = sub {&$n." ".&$m." ".&$o."\n"};
print &$s;
$n = sub {2};
print &$s;
[download]