Not to be a Debbie Downer, but there is a thread on this forum from 2012 about the fiberglass chainplate failing on a 430 leading to a dismasting, $35K to repair (including new spars and rigging).
That said... You always have to assume the worst if you don't know specifics about the maintenance history. Assuming that it still has the original rigging that it is older than the recommended 10 year replacement cycle for SS Wire Rope, and that if maintenance was neglected you will have seized cotter pins or other hardware due to dissimilar metal corrosion. With that in mind you really want to unstep the mast to replace the rigging... I wouldn't want to be up the mast in a bosun chair fighting with crusty seized hardware, total nightmare. If a rigger ran into such problems trying to replace one shroud at a time, the labor hours would eventually out pace the cost of unstepping the mast and doing all the work on terra firma.
I'm no expert in buying spool wire and hardware from Europe but I can only guess that, due to the economic situation in Greece, the opportunity exists to save money purchasing supplies in bulk via advance price contract and having it available on the ground when you land. Like Jack Daw mentioned, you'll get top notch service in Greece if you have a local rigger do on-site measurements and swage your fittings right there.