Guild Wars 2

For example lets say a skill gives me (hypothetical)

Regeneration – 1000 Healing over 10 seconds.

I grab some Dwayna runes for 20% Regeneration duration. Is the new skill now :

1000 Healing over 12 seconds

-or-

1200 over 12 seconds

So does Regeneration duration simply make the effect last longer but heal for the same amount, or last longer with the same healing done per tick effectively increasing the healed amount?

It would go to 1200 over 12

Your Regeneration boon will always heal you for a certain amount every ‘tick’ (second). That amount is based on your level and Healing Power. By extending the duration of the boon, you’re increasing the number of ticks you receive. So yeah, 1200 over 12.