The "reparent" command:
Usage: fossil reparent [OPTIONS] CHECK-IN PARENT ...
Create a "parent" tag that causes CHECK-IN to be interpreted as a
child of PARENT. If multiple PARENTs are listed, then the first is
the primary parent and others are merge ancestors.
This is an experts-only command. It is used to patch up a repository
that has been damaged by a shun or that has been pieced together from
two or more separate repositories. You should never need to reparent
during normal operations.
Reparenting is accomplished by adding a parent tag. So to undo the
reparenting operation, simply delete the tag.
--test Make database entries but do not add the tag artifact.
So the reparent operation will be undone by the next
"fossil rebuild" command.
--dryrun | -n Print the tag that would have been created but do not
actually change the database in any way.