The substitutions are saved in the registry. Designers alone know why.
I figured it out a few days ago. It requires messing with the registry, which can be intimidating, because you can screw up your computer if you do something wrong. However, if you follow the instructions exactly, and only mess with the Scrivener entries, you can transfer them.
See this thread: [url]Any way to import custom dictionary words and substitutions from Scrivener 1?], third post.