There is no 'food grade' ISO as it's poisonous no matter how pure it is.
If you have real 99.6% Ethanol then it's not denatured and would say on the label if it was. It won't likely be grain alcohol tho but ethanol made in a factory. Medics used to call it Bug Juice and it's fine to drink but not advisable to drink it straight. Pure alcohol absorbs water quickly so after one use even with distilling to reclaim it it'll be down to 95.6% or lower but still fine to drink or use to make more oils. A desiccant like zeolite is used to remove the last of the water to get higher purity.
If it's RSO type oil you're after then soaking in solvent with heat will extract all the plant compounds. Will be crap to smoke but it's what you want for medical/edible use. If using ethanol you can leave a little of it in the oil to dilute it to make it easier to handle.
In Canada now you can get up to 14 years in the slammer for making oils using flammable solvents so I'm good to go making my cocobudder.