For names of DITA2Go-generated files, DITA2Go is more restrictive than Windows. Only alphanumeric characters and upper-ASCII accented characters are allowed; no punctuation at all (except a leading underscore for starting topic files), and no spaces, unless you explicitly override these restrictions. See §1.1.2 File, directory, and path names.
The ability to respecify output file names is available for a single purpose: to allow creation of files that external software tools need to have named a particular way. Doing so works well for that purpose. Do not try to rename split files unless you are constructing an automated system. Why? Because our experience shows there is a very high probability of name collisions.
Note: Renaming an output file outside of DITA2Go breaks any links to that file; however, see §28.6.2 Enabling links to renamed or relocated files.
§43.2.1 Renaming individual output files