I assume still not available( to expensive) for hobby use?

You are talking about flash tool or mod that needs to be done on ECU? Or both?

Hello together.

I have following idea in mind, as reverse-engeneering the Bootloader will be too much effort(for now):
1. MED9.1 is basically a MPC562 with attached M58BW016DB NOR Flash
2. Goal is to make that flash writable.
3. There is a Application Note which mentions some library code, which allows Flash R/W with a MPC555 with M58BF008. See attached PDF
4. Both Flash and Microcontroller mentioned in the App-Note are nearly same, so i would expect that this library will work.
5. I have already a Custom-KWP-Service and a C-Compiler ready to use.

I would implement a custom KWP-Service, which would expect a memory address and size. Then it would read the ram from this location and write it to flash using the library code above.
Filling the ram is already possible with the "writeMemoryByAddress" KWP-Service.

Unfortunately i cannot find the "STMICROELECTRONICS SOFTWARE DRIVERS" which are mentioned in the appnote yet. However it should be possible to obtain them from somewhere.
I know there are some limitations like interrupts/watchdog etc, but i can disable them before writing the flash.  Also my code can run from RAM to avoid any collisions.

@prj: What do you think about following "implementation" idea?

Yes you did, however i dont need to execute from flash anymore.

As i mentioned before, i have developed custom KWP services. I can R/W RAM and i can also execute from RAM. So idea would be:
1. Compile my "Flash-Writer-Code" into a binary blob.
2. Write that blob into ram using writeMemoryByAddress
3. Use my custom KWP-Service to execute that code in RAM
4. Code will then perform some changes on the flash and then reboot the system.

I know that the code needs to follow certain rules to be executed correctly in RAM(jump addresses etc).