@Davidsteel1
I already explained why he's saying that. If it was regular time travel, there would be two Zerefs in the past. Most importantly, it wouldn't take away Present Zeref's immortality, which is his main goal here besides defeating Acnologia.
And I don't see Zeref saying that he will reset and destroy the timeline. He says that the world (present) will crumble and his world (new life) will start. This is obviously just an expression. His exact words in the explanation are:
"With Mavis' power, I can return... to my normal self..." <- He's going back to the time where he was a normal human.
"Neo Eclipse. I'm not talking about traveling to the past or the future." <- The name makes it a clear reference to the Eclipse Gate, that can and has been used in the series to physically travel to the future or past, that is why he mentions both despite his plan only involving the past. He's saying that what he's going to do doesn't work like the Gate.
"I'll live my life over again, by resetting time. I'll return to the time before I became immortal." <-He's "resetting time", an expression meant to say he is rewinding time to the point before he became immortal. Resetting time would mean starting the timeline from zero, which is obviously not the case. As I've said above, in practical effects, he's going to rewind time to time travel mentally, not physically, which gives him the chance to change things.
Natsu then asks what will happen to the rest of them in the present after Zeref is gone.
"Who knows? After all, this isn't my world anymore." <-Zeref doesn't know or care, since he will be in the past, in his "new world".
So far no proof of him resetting and destroying the timeline. From what we can gather, he's effectively rewinding time and keeping his memories to change the past. Would this retcon the present? Most likely, but this doesn't warrant a Low 2-C rating more than the character I mentioned rewinding time 8 years to change the past and avoid several deaths, thus changing the timeline, does. Any time traveler from a non-deterministic series could change the past and retcon the present, this isn't considered Low 2-C as far as I know.