If you send the same character who went back in time in the comic but bend the rules of time travel to allow that, it's changing everything, but if you send a character who famously dies in the future back in time, it's not? I hardly think that's changing everything. We're still talking about an X-Men storyline involving a dystopian future, Sentinels, and traveling back in time to change that future. The details are clearly being changed either way and I don't think the exact rules of time travel are important. Granted, it's been a long time since I saw the 90s version, but was Bishop's memories sent back in time or did he physically travel?