Cross-repo replacement while preserving both histories and not doing a lot of manual stuff

repo_magic.md

# Navigate to your existing repository
cd /path/to/existing/repo

# Add the new repository as a remote
git remote add new-repo /path/to/new/repo

# Fetch the branch from the new repository
git fetch new-repo branch-name

# Create a new branch in your existing repository
git checkout -b new-branch

# Remove all tracked files while respecting .gitignore
git ls-files -z | xargs -0 git rm -r --cached

# Commit the removal of all files
git commit -m "Remove all old files"

# Merge the branch from the new repository
git merge new-repo/branch-name --allow-unrelated-histories

# Resolve any conflicts if they arise

# Commit the merge
git commit -m "Merged branch from new repository"

# Push the new branch to the existing repository's remote
git push origin new-branch