IMO, yes on swapping the big ring for a bashguard. However, not all bikes can handle DH. Steep, rocky, technical trails can tear apart XC bikes pretty quickly. I see it happen all the time at lift accessed areas. People show up with XC bikes and end up walking down the hill with taco'd front wheels, flat tires, blown out forks, etc... It's better to rent a DH bike for the day if you don't have one and save your own for XC riding.