It's all down to what you are trying to achieve.
If you are trying to adhere to a standard - e.g. build a C63 replica - then you should listen to the helpful advice given here.
If you want to make your own creation - then just go wild in whichever direction your imagination takes you.
Ultimately, you are the only person who should be happy with the result, based on the targets that you have set for yourself.
Which is why your comment about the car being an AMG-Line as 'justification' for the AMG boot badge prompted the response that it did - if you are going by anything that MB have intended for this car, then the boot badge shouldn't be there, but if you are doing your own thing, then how MB called the model in the first place is totally irrelevant. A response along the lines of 'I know that my car would have never had an AMG badge on the boot, but I like it this way" would have mitigated the come-back.
My other bit of advice is that you should be clear with yourself and forum members that this is done purely for fun. In terms of commercial gains, it can go either way. When the time comes to sell the car, an enthusiasts (or forum member) might like what you have done and be willing pay a bit more for your car, but equally a potential buyer looking at your (hypothetical) ad on eBay or AutoTrader or Gumtreee might consider the car to be 'butchered' and will avoid it at all cost (definitely any dealer taking the car in as Px will not appreciate your work). So it will help if you are clear that you may or may not get your money back when you sell the car, either way it makes no difference to you - in the same way that AMG owners ignore depreciation on their cars - it's not an investment, and as long as everyone is having fun, it's all good