[Andreas]

Try this

userdata_presave

PHP Code:

if ($this->fetch_field('posts') >= 50)
{
    $membergroupids = $this->fetch_field('membergroupids');
    if ($this->fetch_field('field5') == 'A' AND strpos(',9,', ",$membergroupids,") === false)
    {
        $this->set('membergroupids', "$membergroupids,9");
    } else if ($this->fetch_field('field5') == 'B' AND strpos(',10,', ",$membergroupids,") === false)
    {
        $this->set('membergroupids', "$membergroupids,10");
    } 
}