Is there a way to automate Spectral Frequency editing?

Automation is generally a bad thing, especially in audio processing, as all audio is different. That's why you will find very little of it in Audition - it's generally something you'll find only in consumer products.

But in this instance, it sounds as though you are trying to use an inappropriate tool. If you want to limit frequencies above a defined point, then using the multiband compressor is a much better bet, as it will do all the work for you:

Set the frequency appropriately, and adjust the threshold slider until you get the degree of reduction you want (red compression indicator). It's set pretty low in this example, as there's very little content at that frequency to limit, and to show you the indicator at all, I had to set the limiter to zero. The other thing you might want to do is set the ratio to be somewhat higher, depending upon how rapidly you want levels above that frequency to attenuate. 10:1 is more like it for hard limiting - there isn't generally much point in going beyond this, and although the control goes up to 30:1, you'll be hard put to discern any difference.