Just yesterday (I think it was) someone was talking about having a very tart beer after adding raspberries to secondary and needing to add some sweetener. So, I think that fermenting out the raspberries will give you a very sour/tart flavor without adding any souring.
If you want to add lactic acid or acidulated malt, that's usually done in the mash. You could add some citric acid at bottling, though, I'm sure.
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