Both but primarily the latter (risky). I see inside boards every day and there is almost always voids around all inserts incl tracks
fibreglass x1 wrapped around, puddle of resin n qcell mix then push the tracks in.
you'd only need to hit that part and u may have created a water to core path
also depends on what tracks - a US box style that's basically a bit of solid rectangle is very different to flanged style like chinook 16" which has no fat there to cut into
I know it could be done with care and moulding the square after cutting it but my reply was for anyone who later reads the thread and thinks router v tracks in any old fashion is ok