Is "website" what you wanted? Just use "%20" instead of white space (" ") in the URL:
@ShadowWizard has suggested a useful site for URL encoding (and decoding) all sorts of potentially problematic symbols (also including
@, crazy combinations thereof, etc....) Just be sure to avoid encoding the functional symbols your browser needs to read as-is instead of decoding.
IMHO, the five-minute window for editing comments is plenty. If you really want to change your comment after the edit window closes, you can delete it and post a new one. Probably wiser to stick with a workaround than to ask for a UI overhaul to enhance comments on SE, which de-emphasizes comments in general.