Is there anywhere a function, built in or not, that will mark (user defined) newly created edges, or leave the newly created edges highlighted for me to then mark or manipulate, if: The edge was made using a knife project cut, a slice operation in HOPs, a bool tool cut, a carver operation, etc...? I see many ways this could be used. it seems like it should already be an operation option already and i feel like i'm missing something fundamentalobvious. Any insight or direction to point me in would be appreciated.
If you cut with the knife for example, the new vertices are selected, you can either save as a vertex group (CtrlG) or mark seam (U), but I've never heard of being able to select them automatically afterwards if you've not done that. But if you use a Boolean modifier for example, the carved part won't be selected.
For the Knife tool, see the answer from @moonboots and for the Boolean modifier: well, before the modifier is applied there are of course no new vertices/edges selected because they are not yet created.
If you want to apply the modifier and mark the newly created vertices or edges as seams or put them inside a vertex group, there is no real automatic way of doing it, but a kind of workaround, you have to do two things before applying the modifier:
The object that you want to be cut needs to have no vertices selected in Edit Mode.
The cutting object needs to have all vertices selected in Edit Mode.
If you now apply the Boolean modifier and go into Edit Mode on the new object, all new vertices from the cutter are selected, while the original ones are not. Now you can either assign them to a vertex group with Ctrl+G or mark them as seams with Ctrl+E > Mark Seam or U > Mark Seam.