To change the initial splash (from power-on), you'd need to get that pixmap embedded into your EFI. However, with the recent changes, any of these systems after

To change the initial splash (from power-on), you'd need to get that pixmap embedded into your EFI. However, with the recent changes, any of these systems after initial EFI can alter the framebuffer and have that persisted up until wayland/xorg/etc. Pressing a key to get the "full dump" is in fact how plymouth works, which many Linux distributions use from the kernel up until gdm/display-manager.