$re = '/(?m)(?<=^[^:]+):/m';
$str = 'id : AA:BB:CC:DD:11:22
connectionStatus : CONNECTED
hostType : WIRELESS
authType : WPA2/WPA3+802.1x/FT-802.1x';
$subst = "=";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php