@MarkT
Thanks for the advice! I used both methods by now, because I bootloaded a new chip and then only changed the fuses of the existing one.
(when burning the bootloader I was slightly confused at first: The standard extended fuse setting was 0xFD (B11111101) instead of 0x05 (B00000101) as suggested everywhere on the internet, but I still changed it to 0x04 (B00000100) as suggested by the tutorial. then I bootloaded the chip and inside of the arduino IDE avrdude gave me an error massage saying something like: failing - this code is deprecated, you probably want to use 0xfc instead of 0x04 (double check with datasheet first). Then I looked at the efuse settings in the chips data sheet and translated the hexadecimal code (seen above) to binary.
I came to the conclusion that the last three bits (that are essential for BOD) stayed the same and the rest changed from 0s to 1s. I then replaced 0x04 with 0xFC (B11111100)and everything worked, as well as the blink sketch to test functionality.
So I guess I successfully changed the BOD level to 4.3V. I just thought that was interesting, because I couldn't find any reference to this change whatsoever.
I also noticed that the ATmega328p that came with the arduino uno has a high fuse setting of 0xD6, even though the arduino uno standard bootloader setting is 0xDE, which is kind of weird.
@TomGeorge
Thanks for this idea!
I might use a multi pole switch and elegantly hide it on the back of the computer casing instead of plugging a headphone's plug into the front panel audio jack as I intended before.