Effect Interpolation/Lead In

Is there a way to lead into a particular effect? For example, I’d like to to change the tempo of a track at the 00:30s position. However, I don’t want the change in tempo to be immediate, I want the tempo to be slowly be adjusted over an amount of time(eg. 10 secs, from 00:20-00:30) until it hits the maximum value I specify. This is usually known in other programs as transition interpolation. Is audacity capable of this?

You need to use Audacity 1.3.13.
There is an effect called “Sliding Time Scale/Pitch Shift”.
To gradually increase the tempo and then stay at that tempo you would process in 2 sections - the first section would be the gradual speed up and the second section would be the constant new tempo. This effect is quite a lot slower (processing time) than the regular “Change Tempo” but much higher quality.

This works well with changes in tempo, thanks for the suggestion. It would be interesting if audacity could do this with multiple effects(perhaps using keyframes) to transition from one value to another.

It’s possible to fade-in most types of effect, though the way to achieve it depends on the effect.
For example, to gradually increase the amount of reverb on a particular track, make a duplicate of the track and apply the reverb effect to the duplicate (all reverb and no dry signal). You can then use the “Envelope Tool” to fade in/out the reverb track as required. This method will also work with several other types of effect.