I'm wondering if anyone has ever gotten their account reset before?
Yes, but the ways to do it are no longer in effect. As someone mentioned earlier, the staff member who used to do it on request is no longer available, and the only other way it could happen (that I know of) would be to run afoul of the ToS (and I'm pretty sure they aren't any staff doing that, either.)
I'm wanting to do it purely for enjoyment purposes to see how long I could remax a manifest knowing what I know now...
if this is not possible, would I have to re-purchase the game? And even then, isn't it still tied to your origin account?
I will surmise that your main account is an Origin one. You would need to create a new Origin account, using a new e-mail address. You could then start from scratch on that account.
You shouldn't need to purchase another copy, although the convoluted way digital rights are handled may make it impractical to get around that if you only own a digital copy. The second account would not be associated with the first in any way. It would be considered a separate Origin account under a separate ID.
PS 3 players have the easiest time, by far, creating second accounts, as that's literally all they have to do.
Xbox 360 players get kinda boned, as they have to pay to maintain a second XBL Gold account in order to start a second manifest.