@my_array_2 = map { s/^CHOP_ME_OFF_//g } @my_array;

##</code><code>##

@my_array_2 = map { 
   /^CHOP_ME_OFF_/ ?
      substr($_, length("CHOP_ME_OFF_")) : $_
} @my_array;

##</code><code>##

@my_array_2 = map { local $_ = $_; s/^CHOP_ME_OFF_//; $_ } @my_array;