How do I...
 

How do I create an Archetype for the Summoner?

And how can I copy a weapon created with the Custom magic Weapon tool and get copies of it.

Are you trying to create a new archtype or assign one to a Summoner?

To allow other characters to use a custom created weapon, it would need to be created in the editor and assigned a unique name.

I'm trying to create a new archetype.

Tools -> Launch Editor

Files -> New Data File

Go to the Archetype tab and select New (Blank) then start making your new archetype. You can use New (Copy) to see how other archetypes are done.

You'll need a unique id (this doesn't have to start with 'ar' but its easier to keep track of if it does) and a name. When done, hit "Save" then "Test Now". If it compiles ok it'll be available to use in HL.

This is not available, I'm sorry to say.