Apply kernel_menuconfig changes to .config in incremental build

Hello
I have already modified some parameters inn kernel via

kernel_menuconfig

and it changes the appropriate target file config-5.10 somewhere in repo as it expected. However, I don't see a way to apply these changes to the root
.config in incremental build.

Probably, i don't need it but i cannot explain why target/linux sometimes treated as unchanged, so no kernel recompilation occurs.

Seems, guide
works only for building from scratch....

BTW, related question. User expectation that
target config is 'consistent' with generic one. I.e.

make kernel_menuconfig

will return target config unchanged, provided no changes were done by user. In reality, some strange merging with generic one done somewhere
there
and i don't understand why i obtain difference all time.

Therefore the question is: how ideally this tree of configs is supposed to work? How target config should be related to generic?