When you are trying to repair a structure there are some rules to the restoration process that we here in the northeast use.
I can't speak for others but only for what I've been taught by the men who do it everyday from a very well known and respected restoration company.
One rule is to try as best you can to save as much of the historic fabric as you can.
Why would you cut away more than needed anyhow?
It would be just more work.
Every restoration job should include keeping the water out when it's done, of course that goes without saying.
Some restoration jobs rules are that you only repair what is there to the same type, size, and style of what was there when it was first built.
Sometimes we see things that we'd do differently now, but if we're restoring then we restore was was there, not improve the way it was constructed.
If we improve it then we are not restoring it, we're improving it. And this changes the character of the original structure.
These are all things that we have to weigh and see what we need to do, want to do, or should do. It sometimes depends on what the customer wants, depending on the intended future use of the building.
Some people don't care if it is truly the "same" as it was. And therefore you don't have to do it the same as the first framer did.

Scotty, if you want to add scarfs to the bottom of your post to make it taller, for your workshop, then I don't see any problem with you doing that.
As long as it is done correctly and that means that each post's new bottom is secured to some part of the foundation to prevent it from moving should any outside force, like wind, be present.

If your frame is stable then there shouldn't be a lot of thrust at the post base. And if there is any then the proper joint and pegs should be used to resist this thrust. And if it's secured to the foundation you'll probably overcome that thrust anyhow.

Hopefully you'll be able to create the workshop you want.....

Jim Rogers