We've been modifying our brains since we discovered alcohol. We have a very large number of ways to modify brains right now - from various psychoactive drugs to surgeries to even directed therapy (which can, over time, cause changes in neural pathways).

It's not a matter of "can/can't", it's a gradient of capability. Over time we will be able to do it more easily; in more complex, targeted ways; and with fewer side effects.