Fuses in the sketh ?

Projects Programming
1

i use atmega644pa-pu with external osc YIC 16.0000 and yesterday i had read about FUSES but i'm not sure about getting my nose into that ... really i'm not sure about doing this for this moment because i have one mcu and i do not want to destroy it , not for now
it is possible to change those settings in the sketch (*.ino) ??? if something is wrong to insert a new sketch and everything is ok ???

default from AVR® Fuse Calculator – The Engbedded Blog

low_fuses=0x7f
high_fuses=0xd8
extended_fuses=0xcd

i wish to get rid of CKDIV8=1 not to divide anymore and JTAG
and i do not know

in the features
in the list's of int rc osc, boot flash section size, and brown-out what should i chose but i will read about that

question if i insert this into my code it will take affect ???

low_fuses=0xC2
high_fuses=0xD9
extended_fuses=0xFF

or is there any way to get rid of CKDIV8 and JTAG SAFELY !!!! XD

2

inside my ...arduino/hardware/bords.txt i have this

############################################################

atmega644.name=Sanguino ATmega644P ok

atmega644.upload.protocol=stk500
atmega644.upload.maximum_size=63488
atmega644.upload.speed=38400

atmega644.bootloader.low_fuses=0xFF
atmega644.bootloader.high_fuses=0xDC
atmega644.bootloader.extended_fuses=0xFD
atmega644.bootloader.path=atmega644p
atmega644.bootloader.file=ATmegaBOOT_644P.hex
atmega644.bootloader.unlock_bits=0x3F
atmega644.bootloader.lock_bits=0x0F

atmega644.build.mcu=atmega644p
atmega644.build.f_cpu=16000000L
atmega644.build.core=arduino
atmega644.build.variant=standard

some lines that changes my fuses ....... its that right ???
the fuses from this file are not the same with the default ... that means every time i burn the bootloader i change the fuses with the one from my file ????

3

Yes, easiest way to reload the fuses is to re-burn the bootloader. Fuse definitions are from the settings in boards.txt.
You can also use this:

You cannot change the fuses from a sketch, a Programmer has to be connected to change them.