I have been using a 1UP rack to carry two Como's with fenders and did not have to trim the rear fender. I simply lowered the spacer on the arm that supports the rear wheel. I also added 2" wide velcro straps to add additional stabilization on the front and rear wheels.
I don't think you had to...
Check out this thread: https://electricbikereview.com/forums/threads/pretty-cool-specialized-training-video-for-bike-shop-mechanics-to-trade-out-displays.32138/
I carry two Como 5's on a 1up rack and have lowered the spacers on the arm that secures the rear tire so that I don't need the foam pads under the fenders. It works just fine.
I use a 1Up rack to carry two 2021 Como 5's with fenders. I adjusted the cross bars on one arm so that it still puts secure pressure on the tires, not the fenders. Works great with no problems.
What about damage to the finish where the clamp holds the frame? I would think over time the paint would get damaged from vibration. Nothing touches the bike frame on my 1Up rack.
I've heard that concern in some youtube videos on chain maintenance. I use compressed air to blow water off my chain after a wet clean and haven't noticed any problems so far.
We have Topeak racks on an XL Como 5 and Large Como 4 step thru. This is what we bought : https://www.amazon.com/gp/product/B000FIE3WI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
We went with the GCS-3 Large purchased from this Ebay seller. About $20 cheaper than Amazon: https://www.ebay.com/itm/202810351014
So far very happy with them.