How do I edit an existing instelled product's options?

[newhere]

I'm pretty new to this so sorry if this is kind of dumb.

I see in my product.xml where I can add a new "setting" tag nested in the "settinggroup" tag because I want to add a new variable to make it available to an installed product.

I could edit the xml, then uninstall and reinstall the product, but I do not want to do this.

How can I update the "options" (which ultimately appear in vBulletin options in the admin panel) of an existing product in order to define a new variable?

E.g. I would like to add:
<setting varname="newvariable" displayorder="20">
<datatype>number</datatype>
<defaultvalue>10</defaultvalue>
</setting>

To an already installed product.

Also, what are valid "datatype" values. (I need a comma seperated list of numbers, will "string" work as a "datatype" value for what I want to do?

Or barring this, is there an easy way to define my own new $vbulletin->options[] variable?

Like some place I can just add global values
$vbulletin->options['mynewvalue'] = "(10, 11, 12)";

(These variables need to be accessable by cron scripts, btw, if that matters. Is there a cron hook of some sort?)