Martin Langhoff [off-list ref] writes:
Something like a manual merge that I could force to happen on command
git-doarbitrarymergeontree -r fromtree:totree [ victimtree ]
That essentially is a simple one-liner:
git-read-tree -m -u fromtree HEAD totree
which is more or less what git-cherry-pick and git-revert do,
except fromtree always is totree^ in git-cherry-pick.