BUG: Enable changing dtype of column where column names are not unique
- [ ] closes #22035, partially #24798
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

@rok is this still active? @WillAyd yeah, I still plan to do this but have to make time. If I'm blocking anything please let me know. :) closing as stale, though we'd still like this when you can comeback; ping to re-open.