the first splash screen is inside the u-boot binary, you can use dd to dump it outside the deot image and reinsert it into your own image, u-boot binary start at offset 8k of the raw sd card
second splash screen is converted at compile time from ppm picture to raw one, hard to extract from kernel binary without proper investigation, best way is to ask clockwork to give us the original picture
easyest way is to disable kernel logo using u-boot kernel parameter (using mkimage to regenerate boot.scr file) and use dedicated splash utils like https://github.com/g0hl1n/psplash
or manual method like https://bootlin.com/blog/super-fast-linux-splashscreen/
compiling kernel is not hard as you think, it’s like compiling any other program with a patch source step more