Installed windows 10 via bootcamp on my MBP running macOS Sierra, but I'd like to expand the Windows partition and shrink the macOS partition, avoiding a reinstall if possible.

I did a search already, but the other questions I've found on this topic are 1) about windows 7 and 2) just suggest using WinClone or similar.

How would this be done manually without the use of paid utilities?

**Edit:** I've used gParted from an ubuntu live USB to resize the windows partition. The only issue now is that windows throws an error on boot. Online sources suggest using gdisk to somehow sync the GPT and MBR tables? 

(I have data backups and mac OS boots fine, so now it's just a matter of curiosity and avoiding a reinstall if possible)