... sometimes there can be "-" character within the string ...

Along with JavaFan, I have no idea what's supposed to happen when a '-' character is encountered, so I'll just tiptoe quietly around that one.

Your apparent first thought about using split doesn't seem so bad: 

>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'

[download]

Update 1: If there might be  * + ? [ ] etc. metacharacter-like things in the  $mod string, best to split on  /\Q$mod\E/i instead.

Update 2: A more general approach (updated again to be a lot simpler): 

>perl -wMstrict -le
"my $orig = 'fEEfoobarFIEFooBarFoEfOoBaRfUM';
 my $mod  = 'FooBar';
 ;;
 my @chunks = split /\Q$mod\E/i, $orig, -1;
 my $new = join $mod, map lc(), @chunks;
 print qq{'$new'};
"
'feeFooBarfieFooBarfoeFooBarfum'

[download]

In reply to Re: Regex + substring by AnomalousMonk
in thread Regex + substring by Anonymous Monk

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