ViaCAD feels a bit too diverse in the way cutting and trimming tools are implemented for solids, surfaces and curves: it not only has a different tool for each kind of entity, but each tool imposes an entirely different approach: curves for trimming solids, surfaces for splitting solids; infinite planes for trimming surfaces; a set of trimming tools for curves... My guess is that those closely follow some set of ACIS conventions.

I wonder if it would be possible to abstract most of those into a simple set of knife tools, as the defunct Electricimage Modeler app did: For cutting/trimming any kind of entity, EIModeler provided a set of "knives" differing in the nature of the cutter geometry only: interactive line, circle and rectangle-type profile knives, that allowed the user to trim/cut just by drawing a bisecting line, circle or rectangle over the selected entity; and pre-drawn curve profile and surface knives, that acted via predrawn curves or surfaces.

As ViaCAD's GUI favours acting on predrawn entities, at the very least it could integrate EIM-style predrawn curve profile and surface knives, I think, with keyboard modifiers to switch between trimming and sectioning plus the current trim side one. In fact, it could be a single knife tool that lets one select both kinds of trimming/cutting entities.