After much searching, I stumbled upon a great example showcasing how to set desired values in key frames:
Misc animation keys
You can find the full source by inspecting that page.
Here is the essential part that has been pasted:
// create a keyframe track (i.e. a timed sequence of keyframes) for each animated property
// Note: the keyframe track type should correspond to the type of the property being animated
// POSITION
var positionKF = new THREE.VectorKeyframeTrack( '.position', [ 0, 1, 2 ], [ 0, 0, 0, 30, 0, 0, 0, 0, 0 ] );
// SCALE
var scaleKF = new THREE.VectorKeyframeTrack( '.scale', [ 0, 1, 2 ], [ 1, 1, 1, 2, 2, 2, 1, 1, 1 ] );
// ROTATION
// Rotation should be performed using quaternions, using a QuaternionKeyframeTrack
// Interpolating Euler angles (.rotation property) can be problematic and is currently not supported
// set up rotation about x axis
var xAxis = new THREE.Vector3( 1, 0, 0 );
var qInitial = new THREE.Quaternion().setFromAxisAngle( xAxis, 0 );
var qFinal = new THREE.Quaternion().setFromAxisAngle( xAxis, Math.PI );
var quaternionKF = new THREE.QuaternionKeyframeTrack( '.quaternion', [ 0, 1, 2 ], [ qInitial.x, qInitial.y, qInitial.z, qInitial.w, qFinal.x, qFinal.y, qFinal.z, qFinal.w, qInitial.x, qInitial.y, qInitial.z, qInitial.w ] );
// COLOR
var colorKF = new THREE.ColorKeyframeTrack( '.material.color', [ 0, 1, 2 ], [ 1, 0, 0, 0, 1, 0, 0, 0, 1 ], THREE.InterpolateDiscrete );
// OPACITY
var opacityKF = new THREE.NumberKeyframeTrack( '.material.opacity', [ 0, 1, 2 ], [ 1, 0, 1 ] );
// create an animation sequence with the tracks
// If a negative time value is passed, the duration will be calculated from the times of the passed tracks array
var clip = new THREE.AnimationClip( 'Action', 3, [ scaleKF, positionKF, quaternionKF, colorKF, opacityKF ] );
// setup the AnimationMixer
mixer = new THREE.AnimationMixer( mesh );
// create a ClipAction and set it to play
var clipAction = mixer.clipAction( clip );
clipAction.play();
The animation consists of 3 key frames [0,1,2] = [initial,final,initial]
The Position array [ 0, 0, 0, 30, 0, 0, 0, 0, 0 ] represents (0,0,0) -> (30,0,0) -> (0,0,0)