One or two additional tips as I wrote the original instructions for changing the anode which appeared on the website having done this numerous times.
It is not necessary for the keel to be fully lowered, in fact it is a bit easier if it is not, but it does have to be lowered sufficiently for the lower bolt through the keel to be accessible.
When changing the anode it is best not to disturb the lower eye through which the lower bolt through the keel attaches. This eye is screwed in and if you don't replace it exactly as it was before the effective length of the ram is altered.
It is helpful if the open end of the hydraulic hose can be blanked off. The weight of the ram cylinder will tend to force fluid up out of this hose thus allowing the ram to slowly 'collapse', i.e. the ram will push itself back inside the cylinder. If this happens the top of the ram will no longer align with its hanger and you will then need to try to pull the ram up so you can fit the top bolt - no easy feat given the weight of the ram and the outside casing will doubtless be slippery with hydraulic fluid etc.
Be careful that the anode is not significantly thicker than the one it replaces otherwise it could foul against the bottom of the cylinder when the keel is fully lifted.
When Tilikum was new I used to replace the anode each year but after a while I stopped doing this as I tend always to leave the boat with the keel up, the anode is therefore out of the water, if I am not on board. Depending upon how much sailing one does, I find that replacing it every 3-4 years is in practice quite sufficient.
It looks like you have all the help you need with this but if you need any more advice I am happy to give it.