Hey y'all, I'm a week and a half late with this, but here's a tool that simplifies the process of loading in new images in the sprite manager in Clover's Star Rod.
Star Rod Spritesheet Image Manager Download
Source Code
It's a fairly simple process, you simply load up the xml file of the sprite you want to edit in your Star Rod mod sprite folder. Then you can load in new images. If the checkbox next to the add button is checked when loading in images, it'll create a new palette to cover all the loaded images. Else it'll apply the current selected palette to the image. After saving the changes, you can see the new images in the Star Rod's Sprite Manager tool.
The program automatically brings down the color count of all imported images down to 16, so you don't need to stress out too much about making it look perfect. If you have any questions about use or the source code, this is the place to voice them.