My experience with GTA V (a retail copy) is that it's also somewhat finicky regarding install and such. There's a decent chance that you'd put all that effort into trying to patch it with legitimate files from steam or some other install trick and it'd come to naught.
Pirated software comes from changing the legitimate software. The implication for you is that Steam seems to download only on a whole-file basis, so any updates or files subject to these changes would have to be re-downloaded anyway, meaning you don't really save any time by taking those pre-existing files.
Really, in sum, I'd just recommend using the default download offering available direct from Steam. It just skips over so many potential problems trying it any other way and will save you a lot of time.
Part of the fun of doing things legally with a paid copy is that you get to pick the easy option where first-time install is usually the only attempt you have to make. Additionally, instead of tempting malware and all number of problems trying to defraud someone of their legitimate labours, you support the developers who make the games you play.
If it's worth it to you to pirate, it's worth enough to be paid for.