before I going to flash a msi motherboard using afuwin soft, I wanna make sure iF boot block flashing is recommend for flashing it correctly? or can I skip it and can flash bios region and NVRAM region both are enough for update
@superb123 - That all depends on what you are updating, and why, and is it stock image or modified etc. If you are just updating stock BIOS, or in general really, I suggest you don’t use AFU if at all possible
Especially if this is stock BIOS, flash using the normal standard method. If that is AFU, then OK, use as indicated by the flash instructions for this model and only use the AFU version provided with the BIOS download.
Really need to know what system is being discussed here for proper answer, some BB contain CPU microcodes, so if you intended to update those then yes /b is required if you use AFU
model "B450-TOMAHAWK"
1
https://www.msi.com/Motherboard/B450-TOMAHAWK
I want to flash modified bios(modify done using using AMIBCP) using afu version 5.10 above. what I modified?"intel virtualization" and "vt-d" both enabled by AMIBCP(was diabled default)
not sure if boot block flashing is necessary in order to enable and activate those.
Sounds like you edited the wrong BIOS then, or you have linked me to the wrong system etc. The settings you mention changing at Intel settings for an Intel CPU based system, you linked an AMD based board
To answer your question in general now, simply changing BIOS default settings does not require Boot Block reflashing, this is contained in the BIOS region and NVRAM only.
Before you do anything now, double check what motherboard model you have, and then what BIOS you are editing! There would not be Intel BIOS settings in an AMD based board BIOS.
ohh sorry for miss spell, it is "AMD virtualization" and "SVM mode"
Thanks, that sounds better 
Rename your mod BIOS back to stock name.extension and flash via USB using built in BIOS flash too M-Flash