Can the Wichita bolt action be rechambered to a more potent round that shares the same bolt face diameter & rim config? Can the bolt be modified? Can a replacement bolt be purchased?

Yes it can be rechambered. Make sure that the dimensions of the new cartridge completely clean up the old chamber like a 284 Winchester or maybe a 7mm-08 Improved. If it is an orginal bolt face it could likely be opened up.
A great smith for customizing bolt specialty handgguns is Greg Tannel www.gtrtooling.com and Kirby Allen (fiftydriver) who also posts on this forum.