Indoor Yucca with brown tips

I have a large Yucca in my conservatory which has developed brown tips, I think probably cause it has suffered from underwatering becuase its grown too big for its pot and the water just runs staright thru'. I am now repotting it, but want to give it a bit of a make over by removing the brown tips on the leaves. Is it enough to simpy snip off the ends of the leaves (to make a new pointed tip), and will the leaves be OK (ie, not die back further).

You can snip the brown off, but they will die back further in time. Your best bet is to cut just short of the green rather than going into it.

Thanks - can I assume that with it now repotted and retaining the water for the roots, will the degeneration of the leaves cease, or once it has started down this route, it will continue, until the whole leaf is brown (and dead).

No, it should stop. The other possibility is that the air has been very dry, but I don't think I've ever had much trouble with leaves browing on yuccas for that reason.