The trick for front guards is to mount the front bracket immediately behind the brake so that the additional washers you will have removed keep the bracket from fouling the headset. Most pictures have this bracket behind the front fork, but that is only really possible with traditional nuts or Sheldon’s mudguard nut. Then as you tighten the rear hidden brake bolt, lift the mudguard up to increase clearance by a few mm. Fitted a set to a CAAD8 in about an hour yesterday. Be careful about angle of the mudguard as it passes under the fork bridge. Too shallow and it will rub behind the fork. Too steep and it will rub in front! Get it just right.
As for cutting the stays – get a very nice pair of cable cutters to do the job. So much easier than a hacksaw. But measure twice and cut once.
SKS guards break when the temperature gets low in my experience; A ride in the -1 to +2 kind of temps plus a wee knock was enough to kill mine.
Did it break at the rear bridge clamp? They all fail there eventually. My last pair managed two winters. I’m not convinced it is the cold, just the tension and vibration. My Tortec ones have lasted.
When they break, refitting is easy as the stays remain on the bike 😀