You need to erase not just the string saying
if($admin==1 or $GLOBALS['isMod']==1), you need to know how PHP works to move that condition :-)
Your code should be:
if($admin==1 or $GLOBALS['isMod']==1){
$pattern[]="/\[[uU]\](.+?)\[\/[uU]\]/s";
$replacement[]='<u>\\1</u>';
$pattern[]="/\[urlc=((f|ht)tp[s]?:\/\/[^<> \n\r\[\]]+?)\](.*?)\[\/url\]/i";
$replacement[]="<a href=\"\\1\" target=\"_blank\">\\3</a>";
}
$pattern[]="/\[font(#[A-F0-9]{6})\](.+?)\[\/font\]/is";
$replacement[]='<span style="color:\\1">\\2</span>';
so you just need to move the closing quote a bit higher...