Convert timber roof rafters to trusses?
No, you can’t change the framing from beams at 4’ on center to trusses 4’ on center, because you’ll overload the exterior wall footings.
Currently, one-half the roof load is supported by the center beam and footings with one- fourth the roof load transferred to the exterior walls and footings. By changing to trusses, you’ll transfer one-half the roof load to the exterior walls and footings.
I’m sure the exterior footings are not designed to accept double their current load.
Why not add beams at 4’ on center to match the one side with beams? This will keep the basic roof system the same. (You should double check the size and span of the ridge beam to insure it’s still acceptable.) You can still remove the center wall, just add posts and footings where needed.