Reserve seat before activate JR Pass?

Can I reserve seat on shinkansen before activateJR Pass? Because I plan to take the fastest type (Hakutaka or Kagayaki, not sure) of new Hokuriku shinkansen. It is mandatory to book seat. But I will use it on my 1st day of pass after I arrive Tokyo few days.

Can I reserve seat on shinkansen before activateJR Pass?

Only on the shinkansen lines run by JR East:
http://www.eki-net.com/pc/jreast-shinkansen-reservation/English/wb/com...

I am not sure whether the site will be updated in time to allow for reservations of the extended Hokuriku Shinkansen, but I would expect so.

Or if by "before activate" you mean "after exchange but before the beginning of the validity period", then yes.

Thank you very much.
I just be aware that it can be exchange before the first day validity. Let say exhange Friday to validate on Monday. So I do it once I arrive.

Thank you Uji. I try again when the line open in mid March. Hope the site will extend the route.

After you have exchanged your pass you can make reservations normally at ticket offices even before the validity period of your pass begins, as long as the trip falls within the validity periond.

Thank you for your reply. It confirms my planning.