welcome, Pinwizkid!
so far it seems like there’s no direct way yet. you can copy cels from one tilemap layer to another in another file, but aseprite will always auto-generate tileset by scanning the layer column-by-column, line-by-line.
if you really need to keep the order of tiles in tileset, there’s this workaround:
- use the script here: Saving Tilesets - #25 by behreandtjeremy (i was testing behreandtjeremy’s edit) to save a tileset file
- open the tileset file, copy the normal layer from it to your target file and convert the layer there to tilemap. that way your tileset will be same as the one in original source.
- if needed, delete the cel in the tilemap layer and copy and paste the cel from original. that way you will have a copy of both tilemap layer content and tileset with tiles in correct order.