Wouldn't making commits on top of their (untouched) commits fine too? When creating PRs, there is a checkbox to allow repository committers to push into the PR

Wouldn't making commits on top of their (untouched) commits fine too? When creating PRs, there is a checkbox to allow repository committers to push into the PR branch. That preserves the original author credit (and any GPG signatures), but moves things along. If that's not enabled, making a new PR based on the same commits works too.