Learning resources about ecu reading/writing

Hi guys, il followed along diesel tuning fundamentals and pratical diesel tuning courses recently.

I started to practice some tuning with winols on stock ecu files found online.

But now i'm kinda struggling because i'm now trying to practice on the ecu reading/writing part and i can't find ressources on this topic (searching both in en/fr).

I know that some ecu can be read directly through obd and others need to be read directly by bdm.

I also heard that obd writing on stock ecu is overall a bad idea, is that true ?

And so, my main question is do some of you guys can send my links to usefull learning resources for ecu reading/writing ?

I'm in France so most of our cars are europeans and have bosch/siemens ecus.

Also i have a mk2 ibiza 1.9 tdi with and AGR engine and bosch edc15 ecu for testing wich i have to read through bdm.

Have a nice day !

And do not hesitate to tell me if something is unclear cause my english isnt that perfect :)

writing over OBD2 is standard industry for updating ECu's at dealership. Dont be concerned. Just make sure it is proper for that specific ECU or you can brick it. Reading most can be read some need jtag for full read.