EEPROM byte/bit-wise writing without erasing possible?

From this page http://www.espruino.com/AT24 I understand you can write whatever number of bytes to an EEPROM.
What I understood about EEPROMs that before writing a certain area (page) needs to be erased first (resulting in all FF) before it is written.
But what happens if I write only a byte?

The reason for my question is this: I want to store an odometer value in an EEPROM and avoid writing too often reducing wear.
What I know from the automotive world is that they are using a certain area all set to FF and (redundantly) clearing single bits in a certain pattern without erasing anything.

Is it possible with Espruino to do the same:
a) Erase a certain EEPROM area (set it to all FF) only once during initialization.
b) Later during lifetime only write single bytes in a way that only zero bits are cleared without doing an erase again?

Something like:

// init (once)
eeprom.write(address,data,true);

// run (every N kilometers / hours)
eeprom.write(address,data,false);