If its' only 1mm in total, then you are only moving the hole back by 0.5mm. I don't see any real problem. In addition the new post studs are longer, so will have less overall force on the sides per unit area than the kit studs would have. If you can visualise the studs pivoting around an axis half-way down the stud, then the normal force will be towards the front of the hole at the top and towards the rear of the hole at the bottom of the studs, so you are moving the rearward force deeper and further away from that thinner area of wood (at least on the low E side).

Just make sure that the body has enough depth to accommodate the longer studs before drilling the wider longer holes, and if so, carefully measure the stud depth and don't go any deeper!