comments Comments are absolutely lovely, not because I'm trying to keep track of who takes my icons, but simply because it's nice to know that people like them, or appreciate them. So please - while it's nice to know who has what icon, I also appreciate a simple "thank you" or "these are awesome".
credit Please, please credit. After all, if no one knows where you got the icon, how can they find more like it? Just put dustedpixels or panpipe on your icon page. On the other hand, if you're using these as icons for a role-playing journal, I don't care so much about credit. I understand that sometimes you don't want something like that in your info.
customizing If it's labeled as a base, it's customizable. And if in doubt, ask. After all, what's the worst that could happen?