Fortunately, from previous recommendations here, I also picked up a universal decapping die today, and found that the trimmer pilot would go into cases that were decapped but not resized, just fine. Looks like if I'm going to trim cases, it's going to have to be before resizing.
Sizing the case will change the size/shape/length od the case, not a lot with a 45 ACP (very little if any though). So, trimming then sizing and the case may not be in spec. I have a Lee trimmer for 45 ACP (bought waaaay back when I didn't know 45 ACP doesn't need trimming) and it was difficult to insert, so I chucked it in a drill and polished the OD with emery cloth and oil. OD came down .001"-.002" and worked well, but very few cases actually were cut/trimmed...
With a properly sized case the case mouth (neck) is smaller than the bullet base (unless it's a bevel base or boat tail), so to insert the bullet into the case, a taper must be installed in the case mouth. By far, more reloaders will simply flare the case mouth to slightly larger than the bullet, so it can be started into the case. Some will chamfer the case mouth, but as noted above, removing metal from the case mouth will become problematic after a few reloadings.
So, for me and my 45 ACP pistols, I toss the cases into the tumbler (for a short time just to get the dirt off, not polish), size/deprime, flare case mouth/prime, charge, seat bullet, deflare case mouth, shoot. Don't bother trimming, primer pocket cleaning, sorting, and I can still get 2"-2 1/2" groups @ 20 yards with my stock 1911 and a bit smaller groups with my P90. But when working up a load/experimenting, I'll sort brass by headstamp and after load is "finished" I go to mixed brass...