the ‘standard’ DRM/KMS methods will work, as per
especially the ‘video=xxx’ method in bootargs. You don’t need to rebuild the kernel, but simply change the bootargs.
I had started this wiki some time ago for a specific use case:
Someone should document (Akira: can you look into that?) the video=xx method. At least if you combine the archlinux link above and my wiki, you should be able to do it (the wiki has instruction to change bootargs without recompiling the kernel)