Modifying the parse tree

[bvchgvbt]

After calling, say, org-element-adopt-elements, do I (or rather my code)
have to do anything to make the modified tree apply to the Org document/
buffer that the tree came from?

I can see that the tree is modified but it isn't reflected in the buffer
it came from, and furthermore calling org-element-interpret-data on the
modified tree at that stage results in an error:

"org-element-headline-interpreter: Wrong type argument: wholenump, nil"

so I'm guessing that, actually, something is wrong with the tree at that
point, which may explain why no changes are available in the buffer if
they should just show up automagically.