I was hired to repair a post-and-beam colonial: replace trim, clapboards, and gutter.  When I removed the trim on one corner, the structural post and ends of the sills (all 8×8) were rotted and dripping.  The rest of the sills are solid, there’s no sag in the building.  Only the bottom 2/3 of the post is bad, where the attic floor beams join (it’s a one-story ell) is dry and solid.  Same up to the top plate and end rafter.

Can I replace the rotted section only, avoiding the joinery above?  Can it be scarfed or  lapped with joining plates?  Even better for a solo carpenter, can I build-up a post in place?  If so, how would that join to the remaining original post?

Weird side-note – this post is visible on the interior.  The interior corner stayed dry, not even a stain on the drywall after years with a bad gutter sending water behind the trim!

I can add photos and dimensions if needed. Thanks