Common practice today to change old wire/rope halyards to all-rope. The original argument was that rope stretched more than wire.. this is no longer true with many of the newer prestretched lines available.
Another issue is whether the rope will pass over the original sheaves. In the case of wire/rope splices there's not usually a problem, in the case of old wire - rope thimbled joints, the sheave may be wire-only. This could be a problem for the rope which needs to be larger diameter if only for the ability to hold onto it. If you find the rope will pass through you're probably going to be OK.
Cuts and wounds from wire barbs are no fun.. change over and you'll be glad you did.. less deck cleanup too - blood stains can be a problem!