Using gentoo-kernel-bin

sudo emerge –ask =sys-kernel/gentoo-kernel-bin-4.19.102 –autounmask
sudo etc-update

     #use 1 to compare existing if needed

sudo emerge –ask =sys-kernel/gentoo-kernel-bin-4.19.102
eselect kernel list
sudo eselect kernel set 3
sudo grub-mkconfig -o /boot/grub/grub.cfg
sudo emerge @module-rebuild

there are 3 ways to apply a useflag in make.conf: this applies that flag to every package on the system, even ones you might not want in separate files under package.use folder (this is what you want): this can be used to apply specific use flags to specific packages the USE environment variable: this only applies the use flag temporarily and next time you build @world that package will be build without that use again