Come on! That smells like C. Not enough line noise, IMO! We obviously need regex :)

use strict;
use warnings;

sub scramble {
    lc $_[0] =~ s{(^.{$_[1]}|.{$_[1]}$)}
      {join '', (split '', $1)[map -$_, 1..$_[1]]}reg;
}

print scramble( "Institute", 3 ), "\n";
print scramble( "Babraham", 2 ), "\n";
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