What if I wanted to also remove the blessing?

Sounds like an XY problem and/or that your example isn't really representative - why do you want to do this?

Anyway, TIMTOWTDI:

use warnings;
use strict;
use Data::Dump;

sub one {
    $_[0] = {abc=>'one'};
}
my $r1 = bless {r=>111}, 'One';
dd $r1;   # bless({ r => 111 }, "One")
one $r1;
dd $r1;   # { abc => "one" }

sub two {
    my $ref = shift;
    $$ref = {abc=>'two'};
}
my $r2 = bless {r=>222}, 'Two';
dd $r2;    # bless({ r => 222 }, "Two")
two \$r2;
dd $r2;    # { abc => "two" }

sub three {
    my $ref = shift;
    return {abc=>'three'};
}
my $r3 = bless {r=>333}, 'Three';
dd $r3;   # bless({ r => 333 }, "Three")
$r3 = three($r3);
dd $r3;   # { abc => "three" }
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And there's stuff like Acme::Damn, but I'm fairly certain that wouldn't be the right solution.

I'm fairly sure there is some perldoc where Larry explains that - contrary to untie - he never saw any sense in implementing unbless ...

Anyway you are always free to re-bless any object into a dummy class.