Atmega328 EEPROM can be written at maximum of 100k times. What if only one particular byte is written 100k times? Does it mean only that byte is affected or all the other byte locations will be affected?
Other bytes will be fine.
Even the 100K is dependent on various factors and might be usable for more: time between writes, temperature, supply voltage, all impact durability.
Tell us about the project.
There are many ways to avoid an EEPROM being written that much.
If you need to update a particular byte every second or every minute, it won't be reliable after a long time. Since that byte won't be reliable, why use it ?
Also make sure you write the byte if and only if the byte is different. Do not ever rewrite the same byte. You can read an unlimited amount of times.