The DIY method which you see in Holland is to make a steel 'A' frame, such that the bottom ends of the A are bolted onto the toerail either side of the mast, which lies on the deck with the point at the bow, so it can pivot upwards. The forestay is transferred to the top of the A, and the mast then lowered backwards with a strong block and tackle attached to the deck controlling the A frame as it rises.
I once lowered my mast by passing the halliard up to a bridge (at Dinard, on the Rance). Nearly got pulled over the parapet!
The additional modification made in Holland is that the chainplates are extended so that shrouds and mast all pivot on the same axis. This supports the mast laterally. The main function of the A-frame is to control the rate of descent after about 45 degrees, when the forestay is close to being parallel to the mast. Another way, that can also be successful, is to attach the spinnaker pole to the mast with a halyard at its end and a tackle from there to the stem, to take over after the 45 degree point.
Many boats up to about 35 ft are equipped in this way, with an easily removable pin in the forestay and a four or six-part tackle led back to the cockpit to control the initial lowering rate.
go and look at boats on norfolk broads to see how this has been done. In particular look at pegasus yachts who have a very good system - the mast can be lowered on the run as I did for many years on my Pegasus 800!
Although there is strain on the tabernacle, it should easily take the strain - if it was built properly in the first place!
The A frame system is the safest way, as the mast must continue to be supported all the way down, and sideways movement (it will want to swing out of line however careful you are) MUST be prevented. Severe damage to the mast and tabernacle can result if the mast swings off line as it comes down.
If sufficient manpower is available you need at least the following: 2 people on deck to support and guide the mast as it comes down, 2 people on a line leading forward at least twice the length of the mast, (preferably more) to control the speed of lowering. One person to go round ensuring rigging does not catch or snag anywhere (particularly roller reefing jib spars which have a mind of their own!).
Raising is the reverse, and you will have a much better idea of whether you need more helpers! Watch particularly that your rigging screws remain in line as the mast rises. It is astonishingly easy for them to capsize. They then bend as if made of plastic - and of course are then useless - and expensive to replace!