The Mast, for new Rigging, off or leave up?

[KeelHaulin]

In regard to pulling the mast down or leaving it up, I would drop it. There are multiple reasons, most importantly is that you are trusting your life to the standing and running rigging to remain intact while you go up to disconnect hardware. If it's "very old" and you don't know what the service history was; well you are risking life/limb on "IF" it will support you. In addition the mast could have hidden flaws or corrosion.

Since all of it should be replaced; simple to drop the mast down and do everything in one shot. The only thing I would not do while the mast is down is run halyards (if they run internal). Easy to get them crossed or tangled with the mast down; but if it's up you will also have a tough time if any are missing already.

If you take the rig down complete you can more closely inspect the mast, spreaders, tangs, etc. Tangs, forks, pins, etc should all probably be replaced with new; since they may have fatigued.

[xsboats]

As a professional rigger, I make it a practice to never go aloft to replace standing rigging. If one shroud or stay is suspect, they all are. The removal of one may not endanger the person aloft if it has been temporarily replaced with a halyard but what if another fails. This can set off a chain reaction that can take down the whole rig. It does not take much for the mast to come out of column with the smallest of wakes , waves , or someone walking on deck. Just like spark plugs, I never just replace just one. Think of the cost of unstepping the mast as being offset by the increased ability to properly inspect the whole rig. Do you really want to cut corners on something that can have such a serious consequence in the event of failure.