One way is to separate the data. Split the string on commas (assumes no email address have commas in them), then split each of those elements into outside <> and inside <>
Edit the data, then rebuild your string.

This seems to work:

#!/usr/bin/perl -w
use strict;

my $test='A <a@bob.com>, B <B@b.org>, Calcutta <O@thehorror.net>';

my @names = split /\s?,\s?/, $test;   #split apart
$_ = [split /\s(?=<)/, $_] for (@names); #make array refs of each
# Above happily learned from merlyn
foreach my $name (@names) {
        foreach (@{$name}){
                print "--$_--";
        }
        print "\n";
}
[download]

--A----<a@bob.com>--
--B----<B@b.org>--
--Calcutta----<O@thehorror.net>--
[download]

And of course, you can edit that as you wish. Of course, if you KNOW one element, it'd be better to use a hash

#!/usr/bin/perl -w
use strict;
my $test='A <a@bob.com>, B <B@b.org>, Calcutta <O@thehorror.net>';

my %names = split /,\s|\s(?=<)/, $test;   #split apart

foreach my $name (keys (%names)) {
        print "$name==$names{$name}\n";
}
[download]

Rebuilding your original list is even easier after you modify it.

my @names;
while (my ($key, $value) = each %names){
        push @names, "$key $value";
}
print join ', ',@names;
[download]

1. No email addresses or names have commas
2. No names or email address have < beyond the wrapper around email addresses
3. Your list always has the entries separated with a comma then a space
4. Your names are always separated from your email addresses by a space.