i haven't used NEST in probably two years or so, but if you add a couple of scrips and select export, it will do so in a certain format.
If you share the format name of the file, i can search for it bcos i had backup of them which i imported after 2-3 crashes.
Im finding it hard to locate what those exported MW list names were, but if i get a hint i can try again.
Also, as far as I recall, you wont be able to do all at once. There was limit of 30 per MW. So you need to import 4 or 5 times, 30 per MW.
Edit: I found MarketWatch.ini file, but this is direct exch encoded scrip list which can also work provided you replaced them. Mostly top 150 in it.