With, I would imagine, further charges if they use the fact that they've read the books/seen the films to give them detailed foreknowledge of events, which is something I've seen a few times.

Particularly if the accuracy persists once they start meddling with things, the 'Butterfly Effect' rarely seems to come into play in this kind of badfic.

'Falling into Middle-earth' should cover it.

Or, in the interests of promoting inter-department wossnames: why not call in an agent of Despatch (technically the combined Departments of Trans-Dimensional Snatching and TD Hopping, as I recall) to help deal with that part? You'd have to write your own for the piece, as no-one's written Despatch for a long time... if you're not up to that, just having your agents phone them and ask if they need to do anything special would be a nice call-out.

hS, promoting wossnames