Simply whip out your regular expressions and come up with something like the snippet below. Really... this was quite simple :)

my $foo = qq{
fnlPfnrff3xvf31vfWrdaMIXMhAHtCALVrMcZ7
Od6cWuetY86lY8aMSnNCEHsxAHMxAFIpAFIpCEopAFIYAFI5CHtSEJxKCOfOjOfOnN6USm
+Mx
ADkQADkpAEoxCFI5GKVrENacOdaMMeetSt6tSsaMKbVzGEopCGNCEMZ7Kb2cjEoIAIw5AE
+oY
ALWte7WchMa9hNa9jLWcY8aEGIxaAHNCAHtSAGNCAKVaAMa1e7V7OYxKGJRSCKV7SqVrOb
+WU
UrWESqV7OSkIALW1hMa9lK2te7W1lL29pbWtlMate7WEGMacY6V7KffGa0pCMXNaQrWclO
+/n
xvfWpcbGpdbOpdbGrd7evdbOlNa1pb17Oe+tY5yUe7WEWsaMY8aMWoxrUpRrGPfOe6WEOZ
+Rz
GL17Md6tWnNKENa9rWMxEKWEKZRKEL1zIZxCAL1jKYxKCPfOc/fehKVzGKVrAJxaALVzCK
+V7
GJRrEP///////////////////////////ywAAAAA5QGqAAAI/wABCBQYQGCAgQEGDgwAIE
+AA
AQACDBw4UGCAAAIEBggQAICAAAMHBggwcCCAAAIDAAggAEAAgQEECgAgYKAAAQIABBAgME
+AA
gQICCAAQIMDAgQMHDhQYQMAAAQIDCAwwcKDAAAMDDBwocEAAAQACDBw4EECAAAEECAQYQO
+BA
gAAEDgwQYOBAAAEEBgAQQECAgQEECgAQYKAAAQEABBAgUECAAAAEBBAAIMDAgQMHDhwYQI
+AA
AQMBBBg4MIDAAAMDDBwoMEAAAQACDBw4EEAAAAEECAQYQOBAgAAEDgwAIMDAgQEGBgAgIM
+DA
AAIFABgwUIAAAQACCBAoIEAAAAICCP8IACDAwIEDBw4UGEBAAAECAwgMMHCgwAADAwwcKD
+BA
AAECAwwcOBBAgAACBAIMIHAgQAACBwYIMHAggAACAwAIIABAAIEBBAoAECCAQAECAgAIIE
+Cg
gAABAAgIIABAgAABBgoMMHDgwIEDAwAQEGDgwIEDAwQIEABAAAEBBg4UGGDgwIEBAAQYOD
+DA
QIECAgQIMFBAgAAAAggIEEBgAAEAAgwcKDDAwIEDBwIAGECgQAEAAAAAEACAAIAABA4kWB
+BA
AAEBDAoMQFBAAIEBBAQIYBBAAIMDAwAIQDAAgAAFBQQIEGCggAABAAQIEECAwAABAAQIYB
+BA
AIMGAQQIECD/AAABAQoGMGhwYAAAAgIYNBggQACBAQQECGAQQIAABgUGABDAYICCAgIECD
+Aw
QIAAAAIECCBAYIAAAAIACGDQoEGBAQIECAAgQICCAgwaHBgAAAGDBgUGECAwgIAAAQwCCG
+Bw
YAAAAQwGIBggQAAAAQYKACAAQIAAAQQIDBAAQAAAAQQACAAgQIAAAAIMABAAQACDBAMECG
+BQ
YACBAQYEGBAAwIAAAQIUDBAgQAAAAQYGCBAggMAAAQIMDDBwAIAABgkECBBAQAABAQIACC
+Ag
gACCAQIEABBAIMAAAAAACAAAQAAAAAAAEAAAgAABAQIACBAAQIABAwAECBAAIACB
};

$foo =~ s#/{4}#//I got inserted!//#;
print $foo, "\n";
[download]

If the above content is missing any vital points or you feel that any of the information is misleading, incorrect or irrelevant, please feel free to downvote the post. At the same time, please reply to this node or /msg me to inform me as to what is wrong with the post, so that I may update the node to the best of my ability.