The best you can do with MarkDownload is edit the metadata/content before saving the “clip” from the extension.
There are some template vars available if you expand “Custom Text” in the preferences pane.
For the title, as well as the front- and back-matter custom text, you can use the following text replacement values. Please note that not all websites will provide all values
{title} - Article Title
{pageTitle} - Title of the actual page
{length} - Length of the article, in characters
{excerpt} - Article description or short excerpt from the content
{byline} - Author metadata
{dir} - Content direction
{date:FORMAT} - The current date and time. Check the format reference
{keywords} - Meta keywords (if present). Comma separated by default.
{keywords:SEPARATOR} - Meta keywords (if present) separated by SEPARATOR. For example, to separate by space, use {keywords: }
There is also support for all meta tags not mentioned above, should the page you are clipping support them. For example, try {og:image} or any other widely supported meta tags
URL information:
{baseURI} - The url of the article
{origin} - The origin of the URL, that is its scheme, its domain and its port.
{host} - The domain (that is the hostname) followed by (if a port was specified) a ':' and the port of the URL.
{hostname} - The domain of the URL.
{port} - The port number of the URL.
{protocol} - The protocol scheme of the URL, including the final ':'.
{pathname} - An initial '/' followed by the path of the URL, not including the query string or fragment.
{search} - The URL's parameter string; if any parameters are provided, this string includes all of them, beginning with the leading ? character.
{hash} - A '#' followed by the fragment identifier of the URL.
Additionally, you can ‘parameterize’ any of the text variables (other than date and keywords) by using the following syntax:
{variable:pascal} - PascalCase: Every word capital
{variable:camel} - camelCase: every word capital except the first word
{variable:kebab} - kebab-case: hyphens between words, all lowercase
{variable:snake} - snake_case: underscores between words, all lowercase