You can do so using SetTile on tile map component, but it will only succeed for instanced tilemaps (otherwise you’d be editing an asset from game world). There’s currently no way to ‘make editable’ a tile map component that started with an asset; I’ll add a call for in 4.8 (it’ll just clone asset UPaperTileMap into a per-instance copy that can then be edited).
UPaperTileMap has methods to get position of a tile, etc…, but they’re not exposed to BPs yet, I’ll bug that as well.
Note: Editing tiles causes a full rebuild of render data at end of frame (so many edits done in same frame should cost no more than a single edit). With a reasonable sized map should be fine, but you probably don’t want to be doing it per-frame to animate a tile or something, for example. For tile animation, I’d suggest laying out tiles in a horizontal or vertical strip in tile set, and using a material to add a wrapping UV offset to texture sample based on time.
Cheers,