In terms of getting the wire through the hole which is smaller than it, you simply file the end till it goes through the hole, preferably with a gentle taper over say about 1/2 to 3/4 of an inch (12mm to 20mm).
Should you only wish to make a small reduction in size, if it is half hard you may get away with 5 to 10% reduction in diameter, any greater than this and annealing is almost certainly required, the simple answer is of course to try it, if it breaks you need to anneal it, if it doesn't, then you don't, unless you need to make sharp bends in it which might also cause it to break. (Please be careful if you are pulling the wire through a draw plate, say with a pair of pliers, a 1mm brass or especially nickle silver wire needs a lot of force to pull it through, make sure you have a soft landing available!)
The real problem you will face is that when it has passed through the draw plate it will tend to curve, the greater the reduction in size, the greater it seems the curvature. If the wire is not too hard, then stretching it will straighten it, if it is very hard then it won't, and the wire will have to be annealed, and then stretched. Some old model railway magazines had suggestions for straightening hard wire by connecting it across the terminals of a car battery and pulling it straight, don't try it, it definitely is not safe.
I have a couple of draw plates and have got to the stage of nearly finishing a draw bench, basically a device where you fit the draw plate and grip the end of the wire with tongs, and pull the tongs with a rope or strap attached to a reel.
Unfortunately I have a few medical issues, and it will be a month or so before I can make any more progress, but when I can get on with it I will write it up on the forum, also I intend to look at other ways of straightening the wire.
Paul