Do not try to rename DITA2Go-generated files outside of DITA2Go.
To substitute a different name for a particular output file, map the original name to the new name (without extension):
[HtmlFiles]
; original html filename = desired html filename
splitfilename = newname
We strongly advise all-lowercase file names, so that they work from a UNIX server, where references are case sensitive. Do not include spaces or non-alphanumeric characters in file names.
You cannot use the [HtmlFiles] section to rename files other than those produced by splitting; not even the file before the first split point, which retains the original DITA name. DITA2Go writes this file even if it is essentially empty.
§27.5.1 Understanding how split and extract files are named.