TOPIC: custom itemid for the registration page

not sure if this will work since i tried to do it manually and the page did not load, but I'd like to load modules on the registration page without having to first create a menu item.

The only way to create an Itemid is to create a menu item in Joomla. That is what the itemid is... a menu item... and that is the only way to assign modules/templates to anything. You assign it to a menu item, so there is no way around that.

I thought on on most URLs you can add ?Itemid=xx and then the page would load the modules associated with that menu id

Yes, but you said you wanted to do this "without having to first create a menu item". If there is no menu item created, then there is no Itemid to use.

When you create the DT Register menu item, all DT Reg links will use that Itemid so you can assign modules/templates to the DT Register pages.

I'm trying to use a menu item that is not DT - it's the Jevent's menu item.

DT Register will automatically associated with a menu item that uses com_dtregister... so you can't set it to use any other Itemid.