The best option would be to contact your stoneware supplier and ask for information on its properties at 1000F.
If you're mixing the clay yourself, or if this is a theoretical question, you may need to provide some more detail:
1) by "unchanged" are you referring to physical properties, microstructure, surface appearance, all of the above?
2) will the body be under some sort of load at 1000F, or in a particular atmosphere, or in contact with some other material?
3) Who is the audience for this document; how scientific should it be; what does it need to prove?