Is it possible in plan mode?
Because I try drag and drop, and didn't work...
Copy and paste is disable
you can "select all" on a page from one site... move this to your library as a new file then drag and drop it into the new site
advanage: lets you save setting like ifame code or designs for reuse
disadvanage: all objects will be placed into one layer only (you can move them) after from the new site... Adobe does NOT save these files by default when you format or move to a new computer so you have to save them yourself (there is an Muse export option)