Answer: Hey, that's two questions. But alright. The first is not standard slur notation, meaning it's not referenced in Gardner Read's Music Notation, the authority on the topic. However, I've seen a vertical slash used to cancel a slur editorially. The slur is there, but the slash suggests to break it. The implication is different, though, from a dotted line slur, which I'd expect to be a more normal editorial suggestion. The dotted line slur means the editor thinks this might be a good place to add a slur, but implication of that vertical line is that the original is slurred yet the editor recommends against it. That I've seen marked by hand in orchestra parts, where the concertmaster is suggesting ignoring a slur found in the original.

If anyone out there has a better idea, let that person come forward.

As for number 2: Brackets in that context would normally mean that the notation or ornament is the editor's suggestion: the editor thinks this could be appropriate though not marked in the original score.

Knowing the identity of the original score would help in answering both questions. Music notation gets progressively more spare in marking as you go back in time. Baroque music was not notated in near the detail of modern music; much was assumed, much left up to the performer. In older music especially one is more likely to see editorial suggestions, or corrections to an earlier editor's editorial suggestions.