Yes, you can change the color value of any spot color except spot colors of PantoneCoated and PantoneUncoated spot libraries.

In Edit Job> Spot Color Replacement, select Enable Spot Color Replacement and then click Edit next to the spot color you want to edit. After saving your changes, you will be able to preview the changes on clicking the Update Preview icon.

If you update a spot color value in Spot Color Library, it will be applied to a newly added job.