Using a 29" wheel in a fork with offset for a 26 wheel will give longer trail thus slowing the steering.
Not if it's shorter as this will negate some/all of the effect on the HTA of having the bigger wheel. My Hummingbirds actually have a slightly steeper head angle when using the rigid fork and 29" wheel than they do with a 26" wheel and 100mm fork – coupled with a fork with a bit more offset they have less trail and sharper sterring, which I feel is generally desirable with a rigid fork. It's all about an interplay between original fork length the frame was designed for, head angle, rake, and wheel size – in the end if it feels good then go with it :-)
The convention is to call it rake when the fork blades are curved, offset when it happens at the crown or dropouts, though the terms to all intents and purposes are interchangeable.