We can specify a range when importing from excel but we need a named range defined within the worksheet to be able to write to it. That should be fixed.
@HenryFeldman: I can't speak for @tomrvincent, but I don't think that proc export for xlsx can do the following. I have an existing worksheet and I want to paste sashelp.class into that worksheet, using a rectangle beginning at cell G10 and do so without affecting any of the worksheet's cells that are outside of that range.