The replacement is managed via a replace client and communication with pillars via the coordination layer through messages initiating actions and data transmission for data to replace.
Replacement communication follows the general communication pattern with an Identify pillar part and the actual replace part. The xsd's for the different messages can be found here.
Note that the actual replace communication is initiated by a client, which also handles the URLs used for the replacement file. Before the Replace File functionality comes into play the client needs a replacement file. This may be locally available and can then simply be uploaded to a URL chosen by the client. Otherwise the client will use the Get File functionality to find the replacement file and have it uploaded to some URL. The client can then download the file, and upload it to a new URL for the Replace File functionality, or the same URL can be used such that the client doesn't need to download and upload the file.