What you are describing is effectively what 2-pass VBR does for you. It makes a first path that calculates the level of change for each particular time in the video and then uses this information to make the best possible use of the available storage space.
It is, however, entirely possible to do the process manually by doing multiple encodings with different parameters. In fact, many formats even support having multiple encodings with different parameters within the same file. This is how you are able to change the resolution on the fly when streaming videos on YouTube and how Netflix automatically adjusts the quality on the fly as you watch to try to avoid buffering issues.
Any professional level encoder should allow you to specify multiple formats for the file in queue and many will even let you specify multiple outputs for one instance of the file. (For example, the render queue in After Effects allows for this.)
In general, I would recommend running a 2-pass VBR and then adjusting the keyframe and total bandwidth accordingly. If you are using a format that works based on the motion in the scene, then generally keyframes need to be more often if the video gets lots of motion artifacts (where it diverges from where it actually should be too much in high motion). If the video is simply too low quality and "pixelly", then the bandwidth generally needs to be raised or the keyframes lowered.