This is a great question. I'm considering doing it on my second copy, I was just now looking at a page about how to do it, it's really easy and completely safe, the worst thing it can do is freeze. Obviously I won't sell hacked items here though, i'd just use it for my map, and to get landscaping items without spending 200+ TBT, lol. I'll probably hack items, but for myself.
i don't think it's as bad as in wild world but hacked items can cause some kind of negative impact. it's mostly minor inconveniences. for example, hacked flowers can't breed. i don't know anything else about it though.
How bad were Wild World hacked items?
There were things called building seeds that could literally brick people's games. It was awful, awful chaos D,: