It will be fine! The wheel sizes for the E46 and E90 are the same apart from the offsets etc, but the wide rear tyre sizes are 245 and 255 respectively. The wider (255) rear tyre just looks slightly more chunky on the rim, but not at all overboard...
This is what the 255/40R17 looks like on the rear of my car:
From the side you can see what I mean by it being slightly more chunky. This is the rear, where the 3rd pic is of the front which is 225/45R17 (same Bridgestone Potenza) - the 245/40R17 would look more like this when fitted on the rear wheels:
Hope this helps! :thumbs: