Boot Jetson AGX Xavier from SD card

Point 1: Please clarify by following the method in Is L4T 32.5 With Jetson Xavier Supported SD Boot? - #19 by WayneWWW. where is the real flashing happening and it would be a great help if you can explain.

Point 2:
If SD card is not a good method for Jetson Xavier AGX, please guide us to create baseline while developing the SW without reflashing, since the reflashing takes a long time.
The intention of this baselines are to have quick functional check, for example if SD card was a method, insert various SD cards as per the baseline SW stages and test the functionalities or demonstrate the SW functionalities as per that specific baseline.

It would be a great help to propose a correct method for creating the baseline for Jetson Xavier AGX SW development.
Thank you