Build Your Own Backbone
As I understand it, Yes, and anytime (though they have removed forge combinations in the past. I don’t see it happening with this item).
1. Right click them and select equip to equip them without choosing stats.
2. Yes, you can still upgrade them later. It even becomes account bound again,
3. The recipes are probably staying after the event.
Somewhere buried in the patch notes they mentioned that the Aetherblades have had the Spinal Blades permanently added to their drop table. As such the backpack and all related functionality they have with the Mystic Forge are likely to stay.
Mine stayed account bound even after picking stats, but I didn’t put an upgrade in the slot out of laziness. I don’t know what effect that will have.
Borlis Pass’ official male cheerleader
Commander by title: Sawnec the Mesmer
I got the achievement even after transmuting the backpiece to my Fervid censer. (I hated the look of the metallic thing, but it had a bit better stats on exotic.)
And regarding the gift of blades recipe, should i try and get it from the npc before the event ends? Someone mentioned it to be cheaper but i’m not sure, and i don’t have craft skills so it will take me a while to get one to 500