Sorry about the confusion Patricks, no you don't need to take the baffling off for the by-pass.
I was just wondering for other reasons: The OEM passage for the pre-throttle breather hose is too narrow on the internal side, narrower than what the external fitting suggests ...
. . 
... and I'd like to enhance the flow by opening it up or by adding a second pre-throttle passage and hose. And most def I'd need to detach the baffling to be able to do that.
For drilling on thermoplastic I'd use dull bits better than sharp ones. I'd first start with a thin bit, say 2mm or so, then use proggressively thicker bits until a last one slightly thinner than the fitting's threaded side. Then the tap.
Remember that even thermoplastic may melt under excessive heat, drill @ slow rotational speeds to minimise heat and do frequent pauses to allow for cooling down.
More great info on the subject: Blow-by and Breather Systems
^ Notice how, paradoxically, blow-by volume is higher at lower engine loads (less throttle pedal).
^ Why high mileage engines with worn/gunked up rings need extra crankcase evacuation.
