Yeah, I could do that, but to be blunt I'm not going to waste my time analyzing the security implications of installing some novelty app. In my opinion, and I am by no means an expert on writing chrome extensions, the more appropriate thing to do would be to tweak your extension so that it only uses the functionality it requires to work. Surely it does not need access to everything in my browser to do what it does.
Look at it this way, if you were selling this thing for $.99 on the android app store and I wanted to install it, and I saw that it needed such broad permissions, you would have just lost out on a sale. Something to keep in mind should you ever move to monetize this in the future.
How else would one edit the image elements in the DOM of every website without access to the websites? That's like being upset that the AdBlock Plus Firefox extension that blocks traffic from ad servers needs access to your HTTP traffic.
Look at it this way, if you were selling this thing for $.99 on the android app store and I wanted to install it, and I saw that it needed such broad permissions, you would have just lost out on a sale. Something to keep in mind should you ever move to monetize this in the future.