Force a remerge using git's plumbings commands

git force remerge.sh

# If remerging a revert, do this to get back your changes
git revert revertSha
git reset HEAD~
git add -A
# And skip to the echo below

# Find the merge-base of an already merged branch
# https://stackoverflow.com/a/4991675/1248889
diff -u <(git rev-list --first-parent topic) <(git rev-list --first-parent develop) | sed -ne 's/^ //p' | head -1

# Performs merge into the cache
# Use the merge_base from above
# If getting an error about overwritting the current tree, do `git read-tree --empty` first
# Attempted --aggressive if your merge has too many non-conflict conflicts
git read-tree -u -m merge_base^{tree} develop^{tree} topic^{tree}

# Resolve merge conflicts.
git mergetool
# Note if there is "deleted by us", you can resolve all of those to 'keep deleted' by running:
# https://stackoverflow.com/questions/45322360/#comment94060841_45322637
git status --porcelain | grep "DU" | cut -c4- | xargs git rm

# Creates a commit using the cache with parents being the current branch and the merged branch
echo "Remerge branch 'topic' into 'develop'" | git commit-tree $(git write-tree) -p develop -p topic

# Resets this branch to the above commit
git reset --hard ABOVE_COMMAND_HASH_OUTPUT