To deepen nut slots without using a file, use a scalpel or craft knife with a sideways scraping action to retain the curved base of the slot.
Make sure the front of the slot is slightly higher to ensure you don't get rings or buzzes. These can be cured by reducing the back of the slot only.
An over-deep slot can be restored with a tiny slip of paper, reinforced with a drop of superglue.
After adjusting a truss rod, use the heel off your hand to rap the neck in a few places to ensure it settles.
Light mineral oil is good for lubing machine heads. Lemon oil for fretboards is just light machine oil with a small amount of lemon oil as scent and can be used in an 'emergency'. Never use pure lemon oil on instruments.
If you use 000 wire wool to take the gloss off a neck, it can usually be restored using t-cut.