preg_replace help

How could I replace the name and YYY ZZZ, AA, BBB, etc. for the same number of letters generatedby some string generator? ZZZ example would be replaced by the Qj3 and e.g. DDaa be replaced for hT4y etc...

.-----------------====-------------------------==  ===--.
|-=[ U S E R T O P ]=---------------.  |
|  `-----------------====----------|
|  1 ZZZ/iND  200.3M  14F  46.8%  80461KBs |
|  2 YYy/iND  70.7M  5F  16.5%  46622KBs |
|  3 Aa/iND  57.2M  4F  13.4%  49353KBs |
|  4 BBB/iND  28.6M  2F  6.7%  32796KBs |
|  5 Ccc/hidden  28.6M  2F  6.7%  67702KBs |
|  6 DDaa/iND  28.6M  2F  6.7%  63206KBs |
|  7 DSQ/iND  14.3M  1F  3.3%  12795KBs |
|- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - |
|  7 Total  428.4M  30F 100.0%  63269KBs |
`-----================---------------------------==------------------'

Code (markup):

 

here is the simple preg_replace example that may work for you.
<?php

$string = 'ZZZ';
$pattern = '(Z{3})';
$replacement = 'Q3j';
echo preg_replace( $pattern, $replacement, $string );

?>