You can now replace a placeholder you already have saved to a scene or multiple scenes. To do so, you simply need to delete the original placeholder. This will automatically open up the re-mapping dialog, which gives you two options:
remove the placeholder from all scenes
replace the placeholder with another placeholder you select
This modal will show you thumbnails of the scene or scenes in which the placeholder you are deleting exists.
Delete from all scenes
Selecting this option and clicking 'Done' will remove that placeholder from all scenes, and remove the pip from Live if it is currently live.
Replace source on all scenes
Selecting this option will enable the drop-down on the right which then allows you to select the placeholder you would like to use as the replacement. Clicking done will then update all the scenes that old placeholder existed in and remove it from live.
Note: The replace functionality will not update Live with the new placeholder it will only remove the old if it was live. You will need to re-take a scene in order to update live.