Atmega328P 8MHz External Clock Has anyone experience configuring the Atmega328P to work with an 8Mhz external clock?

I want to reduce the power consumption of the device. If I just connect an 8MHz external quartz oscillator then simple programs like LED blink still work (With the time delays doubled), but if I try to use communication like UART, then I am unable to. So no programming new sketches.
The easiest way is to use the settings:

Tools > Board > Arduino Pro or Pro Mini

Tools > Processor > ATmega328 (3.3V, 8MHz)

The problem with that is the Pro Mini bootloader is 2kB and has a bug that causes an endless reset loop if you do a watchdog reset.

The better option is to use https://github.com/MCUdude/MiniCore, which includes the Optiboot bootloader, saving 1.5kB of flash memory vs using the Pro Mini bootloader and doesn't have the watchdog bug.

After selecting the correct configuration for your hardware from the Tools menu, do Tools > Burn Bootloader, which will set the fuses on your ATmega328P and upload the correct bootloader.