I sought another solution… and I note that your proposal is much better.
However, the module cssadmin and your extension mycssadmin for pical have a bug (easyphp1.8 + Win XP) with $mod_url.
Here my small correction :
-> going to line 41 :
$mod_url = ( str_replace($xoops_root_path, XOOPS_URL, strtr($mod_replace_path, '\\', '/')) );
$mod_name = basename(dirname(dirname(__FILE__)));
-> replace by :
//$mod_url = ( str_replace($xoops_root_path, XOOPS_URL, strtr($mod_replace_path, '\\', '/')) );
$mod_name = basename(dirname(dirname(__FILE__)));
$mod_url = XOOPS_URL.'/modules/'.$mod_name;
(vive google^^)