Question about Kernel

I just want to modify chromimum_kernel_5_10, completed step is shown in below

– Added some patches in chromiumos/src/third_party/chromiumos-overlay/sys-kernel/chromeos-kernel-5_10/chromeos-kernel-5_10-9999.ebuild

The questions are :

1. In above path, there is an another ebuild file: chromeos-kernel-5_10-5.10.111-r1825.ebuild, what is the difference between 9999 and r1825? Which file will be used during kernel compiling?

(Based on my resaerach on Google, 9999 is “live” but I cannot understand the meaning of “live”. But after my edition, I could see patched are installed from the log. However, I am still confused with the connection among these files)

2. Can someone tell me where is the file(or bash) that contains the information about compiling the kernel? I just want to confirm which instruction calls ebuild.

3. What I need to do for the next step is modifying config. Luckly, I found the bash (kernelconfig). However, I am confused that my edition using kernelconfig will be kept forever(In another word, when I run ./build_img, will the edition of kernel be removed or saved)? This question seems to have connection with 2nd Question.