Modifying the link resolver settings for Elsevier products including Science Direct, Engineering Village, EMBASE and Scopus are done through the Elsevier Admin tool. As an example for ScienceDirect, once logged in, navigate to the Link Resolver options and choose the option called OpenURL-SFX-Standard:
At the resulting page to edit this configuration, add your new LibKey Link URL as shown:
There are additional options on this page to name the link as you would like, add an image and more.
NOTE: Scopus can take up to 24 hours for any updates to be reflected when you make a link resolver change and ScienceDirect can take up to 14 days.
Most other products from Elsevier including Clinical Key, Engineering Village and EMBASE require that a library reach out to the appropriate support desk to make a change. Here is a complete directory of all Elsevier support desks.