Technically, yes, however I would recommend replacing only half with an equal amount. You can make your own pistachio flour by grinding raw pistachios in a food processor, then sifting them through a fine mesh sieve. I opted to use just almond flour, because I found using pistachio flour didn't result in pistachio flavored shells. Plus, pistachios are expensive! Pistachio paste is also expensive, but it's going to provide the most flavor. If you'd like even more pistachio flavor, you can add a dollop to the center of each macaron when assembling them.