It is is possible to allow additional characters to be used for Directories and Filenames. However your filesystem obviously needs to allow it, and you are required to modify the Tridion System Schema.
To modify the system schema, you must edit the
cm_xml_usr.xsd file, located inside
..\Tridion\bin\ and modify the regexp pattern inside the
name="Directory") element to allow whatever characters you want to allow:
<xsd:documentation>Simple type used to restrict file names</xsd:documentation>
<xsd:pattern value="[-a-zA-Z0-9!\(\)_~.&\ ]+"/>