The answer to your question is no, you won't have "Hot Spots". You do need to be absolutely sure that the spackle is fully dry.
My question is why would you want to do this? If your going to buy the powdered spackle, your also going to have to purchase a 1/2" drill and a mixing whip. I find that the premixed compounds shrink less, are easier to use and save a lot of time. For me, time is money.