Human activity (e.g. oil production, underground nuclear testing) does impact seismological events to some degree so butterfly effects are possibly there too.

If he can leave a bunch of computers in the past and there is a strong enough incentive to keep them running indefinitely... could he have software on those specific machines that will produce an output every so many years?

Would there be a plausible defense against the stewards of the machines being able to reproduce the computers state and fast-forwarding it on a faster computer?