Automated xml modifications aren't necessary.
https://github.com/Whonix/Whonix/blob/master/build-steps.d/1150_export-libvirt-xml takes files from Whonix source libvirt folder, which do not have version numbers, adds version numbers to their file names and copies them to whonix_binary folder.
https://github.com/Whonix/whonix-developer-meta-files/blob/master/release/compress_libvirt takes these versioned files and creates a versioned ~/Whonix-Gateway-X.X.libvirt.xz.
From user's perspective...
https://www.whonix.org/wiki/KVM has been updated to make it as user friendly as possible. (Some still minor shared folder related TODO, merging those two chapters.)
Users are advised to download Whonix to their home folder. They don't have to type version numbers for extraction or libvirt import, because we're using "-*". When users are copying and pasting the command for copying the images, the version number is removed.
I guess this is as easy as we can get it for now and I am excited to have KVM Support in Whonix 9. Most likely I soon will provide some very early downloadable pre-alpha test images for Whonix 9.