What r the points i need to note while changing my machine heads?? And any specific thing required to change it other than new machine heads and a screwdriver?
You will need an end wrench as well. The metal used in machine heads is very soft so it is important to use the closed end of the endwrench so that you don't damage the nut.
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Depends entirely on which machines you are replacing with what.

Make sure the big holes are the right size. You may need to drill or ream.

Make sure the little holes are in the right place and you drilled one there, not just hoping the screw cuts its way in.

If it's a direct replacement, life's a lot simpler. Then it's just a screwdriver and maybe a wrench job.

Changing the tuners should have no impact on the truss rod.
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