split can also capture. So if you want all the pieces, the G-strings and the other bits, it could work like this

use strict;
use warnings;

my $line = "GGCTTTCCGTTGTTGCTGGGTGTGGGGGGCGGGCGAGATTGGAAGAGCACACGTCTGA
+ACTCCAGTCACGCCAATATCTCGTATGCCGTCTTCTGCTTGAAAAAAGGGGTGGGGGGGAGGGGGGGCG
+GGGGGGGGGGGGGGAGGGGGGGAG";
my @pieces = split /(G{10,})/, $line;
print "$_\n" for @pieces;
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