Can I use an officially released build of Caddy and have that official Caddy executable load FrankenPHP?
I know you can using Nix for sure. I think Arch/pacman (Arch Build System) and Gentoo/portage (since it is source-based) also have this concept, but I’ve never used it. No clue about other package managers.
The downside is that package updates will require a recompilation, but you can use binary caches to centralise this slightly.