If I read the specs correctly, you'll end up with a mash pH around 3.5 and about 5-6 g/l of lactic acid contributed by the malt.
The first will create some difficulties as it's below the optimum for enzymatic conversion but in general low pH is less of a problem than high, so if you doubled your mash dwell lengths you'd probably be OK.
It will also reduce the solubility of alpha acids and the rate of iso alpha conversion but you probably don't want much bitterness in a beer this sour anyway.
Assuming your beer would have had about 1 g/l of organic acids anyway you'd end up around 6-7, which appears to be in the usual range for sours.
BTW I thought German acidulated malt was produced by a lactic fermentation of wort which is then sprayed onto the malt before kilning. My understanding is that this gets around the reinheitsgebot strictures on additions to beer.