Depending which country you lived in, there is legal consequence for getting stuff from unauthorized source, there are a couple ways to work around your data cap.

Legally:

1. get a external USB3 SSD portable
2. download using internet not capped, ie. your friend or library, mall, etc(remember to limit the data rate so you blend into ambient youtube/streaming traffic) Referencen: Scrolldown for a chart and use 720p/1080p as your rate limit
3. hook up back to your PC and move the game to different local SSD folder.

Shady, really not recommended because of point 3:

1. look up your local law regarding P2P like torrent AND VPN. (well, not every country consider VPN legal.)
2. Make sure you know how internet works, protect yourself/identity. Pick a good VPN provider, make sure they have their own or use good privacy policy DNS, pick a good torrent client that supports magnet link and encryption and choose "forced" option. (means you don't download/upload to client that have encryption turned off. ) And set you seeding cap, (I don't blame you if you choose to not seed cause data cap is real.)
3. Last but not least, pirated game, like any pirated softwares, are exposing you to malware/virus/randomware, etc. They can hide in any possible files you downloaded cause you don't know what else they touched this entire thing to work. So sandbox your environment or playing on low overhead VMs might be necessary.

And, when you can, move somewhere that have good ISP that have no data cap.