You can load an image from url into the tilemap, but you can't have 2 instances of the same object with a different image, so 1 image per tilemap object.
I understand but I think there is a bit of confusion, in DOC says this:
Load image from URL
Load a new tilemap image from a given URL. It is not used until the image has finished downloading, and On image URL loaded triggers. Images loaded from different domains are subject to the same cross-domain restrictions as AJAX requests - for more information see the section on cross-domain in the AJAX object. Data URIs can also be passed as an image, e.g. from a canvas snapshot or webcam image.
In DOC talks about loading a TILEMAP image, but does not say anything about TILESET, the TILESET is the set of tiles that you will use to build the map with the tilemap object.
I want to load a new TILESET in my TILEMAP object.
I understand that you can not have two equal objects with different TILESETS.
That's not a problem for me because I'm just going to have a single tilemap object.
I want to change the TILESET of my tilemap object at runtime.
But there is no action that is "Load new tileset" on the tilemap object.
Load image from URL I think it only loads a new map for your tilemap object, but it does not load a new TILESET for the object.
Maybe I'm wrong but I think it's not possible to load a new TILESET into a tilemap object, in fact, you can not access the properties (width and height) of the TILESET image loaded in a tilemap object.