I don't fully understand your question about the extra failed Stephen/Julia. If you have the plastic curling system then there is a spare lone that you attach to the job halyard so you don't lose it as you pull the sail down the track. Also many people have a spare halyard for spinnaker that can also act as safety in case from stay breaks. Furling line comes off the drum and through fairlead or around stantion to cleat near cockpit. My line slips neatly through a gap where station fixes to deck at front of coach roof so it early is held out of way of feet. It's really helpful to keep the walking way clear otherwise feet roll over the lines and make you slip.

On mast you should have main halyard and topping lift lines one either side to cleats . If you want to lead lines back then the msinsheet can go round a pulley that is shackled to spare hole in mast base or where can't attaches. Similarly topping can be led back through a shackled pulley . In my case I took the line then outwards to pulley fixed to station and back to spare plastic cleat already on the deck on port side as standard . You might need to extend the lines. If you want reefing lines led back to cockpit you will need additional pulleys and cleats that are with fixed to base of mast or you fix new cheek blocks and have clutches at the cockpit. I have only fixed one new cheek block and I bolted it with large penny washer on inside and siccaflex sealant. When using the sealant let it go off partially before you tighten fully otherwise you squeeze it all out!

Roly

Just my ramblings on fixing options:

Start by considering what sort of load the attachment will have to take. Consider shock loads and sudden accidental loads if something else fails. Then think about how bad it would be if the fixing failed. If it's a fixing for a shroud chain plate then you might consider it more or less critical than your gimbaled glass holder. Is de-masting more serious than spilled gin?

Adhesives are great, they hold modern aircraft together, but they tend to be unpredictable unless you control the exact environment conditions and prepare the surfaces etc. Some work superbly others are useless. Be prepared to experiment a little.

Self tappers are easy but don't have great holding force in GRP. They can also provoke hairline cracking in the gelcoat.

Bolt through and use a penny washer or backing block to spread the load. Use nyloc nuts to prevent things working loose. Don't overtighten bolts, you actually reduce the load capacity as you tighten them more.

304 or A2 grade stainless steel might be ok for below decks but I'd stick to 316 or A4 grade stainless for any deck or bilge fittings.

Drilling GRP is easiest with diamond grit drill bits but HSS will work fine (just gets blunt sooner). Don't drill lines of hole in highly stressed parts of your deck/hull. Put tape on the GRP before drilling, it helps prevent your drill skidding about as you start. Drill from the gelcoat side to avoid spalling as you break through. Measure twice drill once!

Use a marine grade sealant on EVERY hole in GRP. Don't use domestic silicon etc. as it won't stand up to the combined salt and sunlight environment for long.

Pop rivets can be backed up using washers both sides but you'll need longer rivets.

Take the fixings supplied with most equipment and throw them away, buy something bigger if possible.

This mostly common sense but if in doubt ask first, look at other boats and see what they have done.

Dave.