knoppix@Microknoppix:~$ perl -E '
> @accts = qw{
>    CAL2345-06
>    CALI123456-09
>    FLOR1234567-01
>    MEGA9988776655-43
>    };
> say for
>    map {
>        s{ (?<=[a-zA-Z]) (?![a-zA-Z]) }{ q{X} x ( 14 - length ) }xe;
>        $_;
>    }
>    @accts;'
CALXXXX2345-06
CALIX123456-09
FLOR1234567-01
MEGA9988776655-43
knoppix@Microknoppix:~$