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

my %replace = (
   R => '{A,G}',
   S => '{C,G}',
   K => '{G,T}',
   ' ' => '_',
);

my %seqs = (
    seq1 => {org => "CAG GTR CAG CTG AAG SAG TCA GG"},
    seq2 => {org => "GAK GTG CAG CTT CAG CAG TCR GG"}
    );

for my $seqKey (keys %seqs) {
    $seqs{$seqKey}{glob} = $seqs{$seqKey}{org};
    
    $seqs{$seqKey}{glob} =~ s/$_/$replace{$_}/g for keys %replace;
    push @{$seqs{$seqKey}{expanded}}, map {y/_/ /; $_} glob $seqs{$seqKey}{glob};
}

Dump (\%seqs);