Hmm. It might be possible, though it doesn’t sound like a great idea to have both D3 3.x and the D3 4.0 default bundle loaded simultaneously, since there will be a lot of overlap. A better strategy might be to load just the new modules you want to use. Like if you just want the new force layout, then load d3-force:
https://github.com/d3/d3-forceBut it might be best to just migrate to 4.0. I know the changelist is long, but it might not be as hard as you think to migrate. And you can always send your questions to the d3-js Google group or d3.js on Stack Overflow and I’ll try to help.