Welcome to the forum.
It is possible that new packing is not required, possibly only requiring an adjustment.
It is technically possible to effect the replacement w/o disassembly.
When I did mine, the boat was on-the-hard and I did a complete disassembly.
For mine, I purchased a complete assembly, w/ four layers of packing, staggered joints, joints cut at 45°, not butt edges, pre-shaped and all four layers fused as a shaped assembly, probably using wax.
That assembly is not required. It is possible to purchase an appropriate length of packing and do all that manually.
So, for mine, an automotive floor jack under the rudder pushing it up into the boat. Disconnect the steering ram and the side to side steering bar. Remove the steering arm. Remove the upper rudder support bar. Remove the packing nut. I also removed the jam nut.
Remove the old packing from the packing nut.
On mine, I used marine grease on the rudder block exterior threads. This makes adjustment sooo much easier. I also run the jam nut up and down, over and over again, until it moves freely.
The standard wide jaw adjustable packing nut wrench sold at West Marine has worked fine for me the half dozen times I've used this tool. IMO it has flimsy construction, but it is good enough. Two wrenches would be better, but I've made do with one.
When I did mine I also removed and replaced the rudder, coating the shaft with marine grease. This step is not required, but it is part of my over-the-top maintenance.
Loosely thread on the jam nut, circular part up and loosely thread on the packing nut.
Replace the upper rudder support bar.
Loosely attach the steering arm, w/ all washers in the same order and the key replaced.
Very important step, pump the floor jack so the rudder is pushed into the hull as tightly as possible.
Push the steering arm down as far as possible and tighten.
Replace cotter pin.
Repeat on opposite side.
Reassemble steering, replacing all locking parts.
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