The DS2431 offers write-protection for its memory pages. See page 7 of the datasheet for details. Addresses 0x80 through 0x84 are the write-protection bytes. Each of these byte-sized memory locations control write-protection for pages 0-3. For example, writing 0x55 to address 0x80 write-protects page 0, writing a 0x55 to address 0x81 write-protects page 1, etc.
Keep in mind that once you set the write-protection up for a particular page, you cannot change the page back to an unprotected page. It becomes read-only with no way to write to the page again.
The OneWireViewer provides an easy way to test the write-protection bytes. Simply write some data in page 0. Then write 0x55 at address 0x80 to write-protect page 0. Then, try writing to page 0 again with different data. It should be unsuccessful.