what are the main differences (apart from speed and power) between the STM32L496RG and STM32F405RG.

[ASmit.15]

I have a PCA design which I'd like to support both devices with min configuration changes in the PCB dependent on the fitted device. I've made provision VACP1/2 options - either CAP or 0R resistor to VSS.

[TDK]

You can get a reasonable answer from this using CubeMX.

https://community.st.com/s/article/how-to-compare-different-stm32-part-numbers-using-the-cross-selection-tool-of-stm32cubemx

They are quite different chips. Unlikely for the code to be compatible even if the footprint can be managed.