$ cat > spw1055482.txt
aaaaaGGGGGG55555
fffffJJJJJJ11111
kkkkkUUUUUU99999
$ head -99 spw1055482.*
aaaaaGGGGGG55555
fffffJJJJJJ11111
kkkkkUUUUUU99999
$ cat > spw1055482
#!/usr/bin/perl -npi.bak   
#
use strict;
use warnings;

for my $offset ( 11, 5 )
{
    substr $_, $offset, 0, q{^};
}
$ perl spw1055482 spw1055482.txt
$ head -99 spw1055482*
==> spw1055482 <==
#!/usr/bin/perl -npi.bak
#
use strict;
use warnings;

for my $offset ( 11, 5 )
{
    substr $_, $offset, 0, q{^};
}

==> spw1055482.txt <==
aaaaa^GGGGGG^55555
fffff^JJJJJJ^11111
kkkkk^UUUUUU^99999

==> spw1055482.txt.bak <==
aaaaaGGGGGG55555
fffffJJJJJJ11111
kkkkkUUUUUU99999
$