read some
(vla-GetProjectFilePath
(vla-get-Files (vla-get-Preferences (vlax-get-acad-object)))
(getvar "PROJECTNAME")
)
and write some
(vla-SetProjectFilePath
(vla-get-Files (vla-get-Preferences (vlax-get-acad-object)))
(getvar "PROJECTNAME")
"C:\\Work1;C:\\Work2"
)