I know Hydrogen burns much faster, so in order to use this fuel in a modern car, the ignition timing tables must be modified. Is it possible to modify the timing so the ignition happens after tdc or close to tdc. I can experiment on a GM Suburban 2015 5.3L. Also, can the fuel injectors able to tolerate hydrogen instead of petrol? Any help will be greatly appreciated. Thank you.
OBDII does not support ECU programming. In some, perhaps many, the OBDII port itself is used to program the ECU but those are proprietary protocols that are specific to the manufacturer and even the specific model.
Generally the tools to update ECU firmware and settings are not available from the manufacturer to end-users, they are sold only to dealers and other authorized service centers.
There are some 3rd party companies that hack the protocols and offer aftermarket "tuning" tools. Some work via the OBDII port and others work via another connector perhaps requiring direct connection to the ECU.
What you're trying to do is likely a very extensive change. You might look into replacing the GM ECU with a DIY system such as MicroSquirt:
This would give you complete control over the engine's functions.