900 tags? Respect! :-)
Just to make my suggestion clear: I'm not suggesting that the "Tag script" button on the "Find script" page be removed, just that a similar button be added on the "My scripts and tags" page. (I should have probably called it "Tag script" instead of "Add tag".) So your current workflow needn't change at all, even if mine did.
I'm not sure I understand how my suggestion would lead to mistakes, or how it would prevent one from looking through and correcting old tags. If that's the case, I withdraw my proposal. If not, I'd still like to see it implemented.
Tag on!