Definitely yes. Databases and compilers have a lot in common. This bytecode is exactly equivalent to a compiler IR. It's called out as such in the OP where the decoupling between front end and backend is noted. Therefore you can construct the bytecode from outside of the database and feed it to the backend (may require patching sqlite to make the entry points accessible).
By analogy, this is really easy in LLVM. You can write the IR you want in a text file and feed it back into the infrastructure. This is used a lot in testing and debugging LLVM. It's much harder in GCC for reasons that never made much sense to me.
There's probably a parser for the format of the EXPLAIN text dump in sqlite somewhere intended for modifying the debug output then feeding it back into the engine. Maybe not documented, but I expect it works fine in practice.
By analogy, this is really easy in LLVM. You can write the IR you want in a text file and feed it back into the infrastructure. This is used a lot in testing and debugging LLVM. It's much harder in GCC for reasons that never made much sense to me.
There's probably a parser for the format of the EXPLAIN text dump in sqlite somewhere intended for modifying the debug output then feeding it back into the engine. Maybe not documented, but I expect it works fine in practice.