I've got more time - actually had to do some office work . . . some clients need to get their priorities straight.
I looked closer at some masthead photos I had taken and now have a clear understanding of what went wrong. Thanks guys for the help - still learning after all these years.
Fortunately, the SS U-shaped halyard fairleads are not riveted to the mast. Those beefy roundhead screws seem easy enough to remove. However, with a second look, there is a U-shackle with a clevis pin connected to the snap shackle, which can be unscrewed, allowing the wire end to slip through the fairlead without unscrewing.
Also see two signal lines already strung through the fairleads. Will they interfere with the wires? Looks like I'm going aloft in a couple weeks, after launching.