I was in the business & this is how I did it.
Stand ladder quite vertical-place your toes at base of ladder legs & reach out arms length-you should be able to grab ladder.Tie a rope
from bottom rung to mast
.Go up carefully & tie top of ladder to radar mount or mast
Don't cut the old cable-they have value-$150 on ebay.
Use slot screwdriver to unscrew 4 captive dome cover screws.Take cover down & put in cockpit
.It will blow/slide off deck
Unplug cable conns in dome,unscrew packing nut & remove cable from dome.
Ues a socket & ratchet to remove 4 dome mounting bolts.Don't be surprised if they are seized in alum. stand. Carry old dome down-they only weigh 25-35lbs.
Now you need a paper pattern of mounting bolts of replacement dome.
Drill new oversize (by 1/8") holes in stand.
Carry & mount new dome,without cover.Use Neversieze on bolts.
Tie a piece of heavy cord to old cable.Tape the plugs on old cable so the result is as small as you can make it.Pull old cable with cord out of mast.
Reverse proceedure to pull new cable up.Don't forget to start at display location with cable,so that display plug
doesn't have to be fed back thru holes it won't fit thru.
If old cable was cut, with a plug/socket arrangement near base of mast,you are in for a treat.My suggestion is to hire a tech to do this soldering job & supply multi pin conn. If you decide to do it yourself,I would suggest a terminal strip(or 2) & use red crimp eye terms. Mount term.strip(s) inside boat.
Good luck /Len