The firmware for the -583 part is same as that of the -483 part. So it doesn't require any modifications in firmware point of view to move from -483 part to -583 part. You can just change the part number in the Creator to build the project. There will not be any problem.
Also, the BLE spec 4.1 is obsolete. So, we recommend you to use BLE 4.2 for all your new applications.
This is not a good answer. Please go back and try to understand why I am asking for this. I know you probably try to quickly answer questions like this but I really need you to focus on the question and understand what is going on.
1) The MILLIONS of -483 units we have in the field will not work with the 4.2 stack
2) We are a medical device company and validating/tracking two separate sets of firmware would be unwieldly and VERY COSTLY. We need to be able to support the -483 and -583 part with a SINGLE IMAGE.
3) A company that obsoletes a part without backwards compatibility is violating the trust of that customer (and we are a HUGE customer of yours)
If you are not able to work with me on this then please pass this upwards.
To expand upon 2) above, I can OTA a -583 image into the -483 and run it. It just need to be built with the 4.1 stack to work completely.