Well, that was a nightmare.
Just too far beyond my skills, tools, eyesight, steadyness of hand...
There are so many problems.
Got the 0R resistor off and almost immediately lost it. It was like a bit of dandruff.
There are other components so close to the antenna socket pads that several times I got blobs of solder stuck on them, causing solder bridges all over the place. Took ages to remove. I tried solder sucker, solder braid, but they were just too crude for the job. Got most of it off, I think. And that was using 0.5mm solder and an illuminated magnifying glass.
Got solder all over the socket itself, making it a very tight fit to get the antenna connector on, resulting in breaking the first socket off the board within minutes and then having to destroy it to get it out of the antenna connector.
Making the solder bridge was just a case of trying over and over, but the position of the 3 pads means that molten solder wants to take the shortest path, and that is to the wrong pad. You can't just put a blob over all three pads because then both the pcb and the external antennas would be connected at once, making the impedance all wrong and the combined gain worse than either alone.
The Pi is still working. I will re-test shortly. Need to relax and let my eyes un-cross.
I cannot recommend attempting this without a stereo microscope, a hot-air solder station, solder paste, and the eyesight and steady hands of a surgeon!