Can we create merge-directives using only one branch

[jk]

Is it safe to create a merge-directive send file using only one
branch, then apply that patch to a child of the branch? What about the
other way, child patch to parent?

For example:
     # Let's say the parent_branch is at revid:abc1051
     bzr branch parent_branch child_branch
     bzr branch parent_branch reference_branch
     # make changes to parent and child branches
     bzr send -o reference.patch reference_branch parent_branch
     bzr send -o parent.patch -r revid:abc1051.. parent_branch parent_branch
     cd child_branch
     bzr merge < ../parent.patch

I'm trying to puzzle out a workflow we could use, and this would help
greatly -- although it is entirely possible I still don't know bzr
well enough.

One of our development environments will never have contact to the
master repository. My hope is that they could do something like a "bzr
send -o patch -r revid:abc1051.. local_branch local_branch", where
"abc1051" is the revision the last time they applied one of the parent
merge-directives.

In my tests, the parent.patch has a few lines in the bundle, where the
reference.patch has tons (1.2Mb vs 23Mb in one case). Even with the
bundle differences, the results between applying the reference.patch
and parent.patch are the same except for the binary file
.bzr/checkout/dirstate.

Thanks.

bzr 1.2.0
bzrtools 1.2.0
gtk 0.93.0
launchpad
svn 0.4.7
xmloutput 0.4.1