[arch-general] kernel compilation

hello members, I'm not used to compiling and therefore even less to compiling the kernel.... I followed the instructions given by this page https://wiki.archlinux.org/index.php/Kernel/Arch_Build_System. after compilation, if I modify/patch file src/linux-4.19/block/blk-core.c, do I have to replace the kernel ? the kernel and all its modules ? or just the module concerned by the change (if it concerns a module) ? regards, lacsaP.