your circuit has BLE, Thermocouple interface, Loadcell interface etc.
The new BLE processor that you are suggesting is ARM based.
The total software will have to be re-written as per the specification, even though the software of ATMEGA may be used for guidance.
This is going to be not an easy job and will be time consuming.
If you are OK with it, we can discuss further about it
Final price will depend on final specifications
Thanks