>perl -wMstrict -le
"my $orig = 'AABBCCDDEEFFGGHH';
 my $mod  = 'bCCDdEEFfgGH';
 ;;
 my @chunks = split /$mod/i, $orig;
 my $new = qq{\L$chunks[0]\E$mod\L$chunks[1]\E};
 print qq{'$new'};
"
'aabbCCDdEEFfgGHh'