AVR Microcontroller board capacitor recommendations
The absolute best approach is (as mentioned in the datasheet for the MCU) to place at least one decoupling cap as close as possible to one power pin. The capacitor should be as stated in the datasheet!

This is a way for the vendors to get insurance if the MCU misbehaves when doing something in some situation while having a particular configuration and while using a specific power source etc.

The further you get from this ideal situation, the more likely the MCU will fail under certain circumstances.

Theoretically, the changes that you suggest do not sound very good to me. For example, six 100nF capacitors is not the same as one 600nF. The reason for this is that the discharge curve is not proportional.

If you ask me if your suggested changes would work for majority of the use cases, then the answer is very likely. As with everything else dealing with the complex subject of electronics, the best thing is to test it out yourself.