I want to copy the same exact build from GrimTools. Is this possible?
Druid, Level 100 (GD 1.1.9.6) - Grim Dawn Build Calculator (grimtools.com)
Welcome to the forum. 
When you say copy what do you mean exactly? Yes, you can get those endgame items by farming for them.
probably not in the way you think/are asking for
either you replicate the build in game manually, like normal, find the items etc make your character as the build lists
or you use GDstash to create the items and transfer to your character/use GDstash to create the lvl 100 character or use the template character uploaded to the forum
or you find and see if the GT build has a forum post with a save file uploaded and then download that copied character
Noted. Thank you for the response. I was looking at the tutorial. So if I mod a character I can play online with friends still right?
So long as it’s not a character from any mod and doesn’t have any modded items, yes. Grimtools is a tool, not a mod so doesn’t affect vanilla characters.