How would modifying your gear be illegal? It's yours and you aren't offering it for commercial purposes or sale. That said I would advise against it. I'd keep the waist pack separate and carry the rest another way. Feces happen and at the worst possible times. I modified my waist pack with straps, buckles and D rings but carry it as a separate entity from the day pack. In the situation you allude to I could dump the pack and still have a full survival load for seventy two hours as I evacuate the area hastily. JMHO