boot loader change

Hello together
How do I change the boot loader by Atmega328P with 16 MHz to a 8 MHz bootloader
Thank you for feedback.

In general, use the same bootloader and make the boards.txt configuration halve the upload rate.
(the stock 16MHz bootloader will run fine at 8MHz, but it will run at 57600bps instead of 115200.)

Thank you westfw
I have changed the Bord.tx so

eigener.name=Eigenes Board(3.3V, 8 MHz) w/ ATmega328
eigener.upload.protocol=arduino
eigener.upload.maximum_size=30720
eigener.upload.speed=57600

eigener.bootloader.low_fuses=0xFF
eigener.bootloader.high_fuses=0xDA
eigener.bootloader.extended_fuses=0x05
eigener.bootloader.path=atmega
eigener.bootloader.file=ATmegaBOOT_168_atmega328_pro_8MHz.hex
eigener.bootloader.unlock_bits=0x3F
eigener.bootloader.lock_bits=0x0F

eigener.build.mcu=atmega328p
eigener.build.f_cpu=8000000L
eigener.build.core=arduino
eigener.build.variant=standard

but I got the error message in the Upload:

System wide configuration file is "C:\Program Files (x86)\Arduino\hardware/tools/avr/etc/avrdude.conf"

Using Port : \.\COM16
Using Programmer : arduino
Overriding Baud Rate : 57600
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: Recv:
avrdude: stk500_getsync(): not in sync: resp=0x00

avrdude done. Thank you.

I think that the fuses are not correct

eigener.bootloader.file=ATmegaBOOT_168_atmega328_pro_8MHz.hex

Ah. If it's an Arduino Pro, it has the older bootloader and didn't run at 115200 before the clock change (probably it was running at 57600 and now needs to run at 28800...)

It is enough only when I change in the Board.txt file the upload.speed on 28800 or I must change something in Makfile