In that case your client will immediately set focus to arena2.
It works because client has GCD, and it can't immediately cast Unholy Presence after Blood Presence. But when you will be already in Blood Presence and click one more time, you will cast Unholy Presence (it's blizzard UI logic, it's okay).
About your question, i think you need to use [mod] things, for the same key but different modes like : ctrl, shift etc.
And you even can't use scripts like /run for changing focus, because BlizzardUI doesn't allow you to use SetFocus() function in the scripts.