The following can only be done when inserting the URL into your email or landing page HTML. There is no global setting to change this permanently.
For example say you have an image asset at the URL: https://na-sjst.marketo.com/rs/164-CZO-458/images/android.jpg
When you insert this link in an email or landing page, you can replace the Munchkin ID with the account string of for your instance: https://na-sjst.marketo.com/rs/mktosupportmybaben/images/android.jpg This link will still resolve correctly and the Munchkin ID will not be displayed.