Puoi fare cosi.
Codice PHP:
<?php
$string = "aer 0,12 ioiodo 9119,98 idido 76 diOISIJ18,65 178,8 9001,123 LLL34";
$pattern = "/(\,)\d{2}(\D)/";
$replace = "XX";
$result = preg_replace($pattern,"\\1$replace\\2",$string);
print '<p style="font-family:\'Courier New\'">';
print "Prima : $string<br/>";
print "Dopo : $result<br/>";
print "</p>";
?>
Prima : aer 0,12 ioiodo 9119,98 idido 76 diOISIJ18,65 178,8 9001,123
LLL34
Dopo : aer 0,XX ioiodo 9119,XX idido 76 diOISIJ18,XX 178,8 9001,123
LLL34