You can still do experiments with some adjustment to your work habits: create the new data structure with a different name, try it it out in some places via renames, and if necessary comment things out. Delete the old one and rename back again when you're done.

The one that still annoys me, though, is having to comment out unused imports in Go. I agree they should always be removed before submit, but in the meantime it's annoying. (Tools that automatic remove unused imports are also annoying in their own way.)