I would first do a lot of measuring and determine what has moved. This would be a great application for an inexpensive water level. Drag it around and note joist elevation everywhere you can. If you set the reference at 12" below the reference point then all other measurements will be plus or minus from that 12"
You are correct in being concerned about the effects of moving just one spot. Once an older house has settled into where it wants to be, moving it is difficult.
There are concrete filled metal posts that you can cut to fit, but there are also heavy duty adjustable columns. I wouldn't recommend a lighter weight adjustable and even the heavy duty should ultimately be replaced with a permanent column. But the adjustable would allow you to ease it down over time.
It would be nice and safer it you could keep the old 6x6 positioned somewhere next to the new post while you work, just in case.
Also, you need to be sure the support under the post was originally as strong as it should be. Hard to determine, but a question that needs to be answered.
Bud
You are correct in being concerned about the effects of moving just one spot. Once an older house has settled into where it wants to be, moving it is difficult.
There are concrete filled metal posts that you can cut to fit, but there are also heavy duty adjustable columns. I wouldn't recommend a lighter weight adjustable and even the heavy duty should ultimately be replaced with a permanent column. But the adjustable would allow you to ease it down over time.
It would be nice and safer it you could keep the old 6x6 positioned somewhere next to the new post while you work, just in case.
Also, you need to be sure the support under the post was originally as strong as it should be. Hard to determine, but a question that needs to be answered.
Bud