You have about 2 choices
If you do this job yourself, or if you have professional rigger do it (my preference), it will probably be done the same way by removing and replacing each wire individually. If I were doing this job, I'd take one wire off and take it to a West Marine and use it as a template to measure for new wire and the end fittings. Replace it and take the next one off. Most West Marine/Boat US stores also have a rigging table that customers may use to cut wire and swage end fittings. Measure a million times and cut once.If need be, connect your main halyard to the bow pulpit to provide temporary support to the mast when you take off the D3 wire, but since the back and forestays would remain in place, you probably would not need to do this.