I have a block for a flag halyard connected to my backstay about 15
feet above my deck. The block has failed, and I'd rather not unstep
that mast to replace the block.

Can I used a bosun's chair and connect the main halyard around the
backstay to lift someone up to the fitting to replace it?

My main concern is placing 180 to 200 pounds of strain on the backstay.
Logic tells me this is okay though, since the forestay carries the
genoa, but before I try, I'd like other opinions.

Thanks!