*K:
Each post had a girt connecting it to the center post, and this girt was also holding up the second floor and or floor joists.
To support the rotten ended post the timber framer put in a good ground block and then a piece of new 6x7 post with a hydraulic jack on top of it. Jacked up the girt to hold up the building, including the second floor, and then put in another supporting post, as a safety just in case the hydraulic jack failed. The post was held in place by some truck straps going from gable end post to rotten post on both sides.
This made the rotten post very stable so that he could drill the hole(s),make the cuts and chop out the section with his chisel, without the post waving all around.
The shorter of the two posts still had a nailer with sheathing hooked to it so that one wasn't as wavy while it was hanging in mid air. But it was still held in place with truck straps going in the gable to gable direction.

Jim Rogers