can I change password char, in password-box in HTML. I want to change it to ■
As far as I know, this can't be done. The password field is rendered natively by the browser.
You could probably build a JavaScript-based workaround, but that would not be as secure, break auto-completion and/or the browser's internal password management, and have other side-effects.
If at all possible, I would stick with the browser's rendering.