Couldn't find any threads talking about this. I do recall seeing one about the front but can't find it...so let's toss some ideas around in this thread for either side.
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I've looked at images of pre-2015 Y51 M's and 2015's and it looks like all you'd need (I mean, it's not a little, but it's not structural) to change is the trunk lid, rear tails, and bumper. The outer edge of the outer tail light (specifically the top and side portion) looks to be the same design...so you wouldn't need to change the quarter panel in the rear. The contours of the trunk itself, where it meets the quarter panel, seems to be identical. Only reason why you'd need a new trunk is because of the tail light cutouts/size.
Here is a pre-2015 Y51 M Rear:

2015+ Y51 M Rear:

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I also think the front is doable...you'd need headlights, grill, and bumper. Hood looks to be identical.
Here is a pre-2015 Y51 M Front:

2015+ Y51 M Front:









