Actually, there should be no fullstops in file name. When you e.g. save "DESKTOP.INF" file to a disk, it's on the FAT directory entry as "DESKTOP INF" i.e. the first part is padded to 8 chars with space(s) and "INF" continues directly from that without any redundant '.' character in-between.
You cannot create filename with '.' in them through TOS or DOS, only with direct disk editing (or corruption).
If this is about STeem host file system passthrough, invalid file name characters should be converted to something valid like Hatari already does (including conversion for unicode file names).