Hi Anupam,
sorry, but as far as I can tell, you can't do that. I would recommend deleting the existing document before you add the new one.
If you remove this line [1] from BaseX source code, then you could use something like this:
delete node collection('sample1.xml')[1]
However, I'm not sure what side effects that would have. Maybe someone else on the ML can tell better.
hth,
Dimitar
PS: you are not hogging the list - it's always nice to have some user feedback :)
[1]
https://github.com/BaseXdb/basex/blob/master/src/main/java/org/basex/query/up/expr/Delete.java#L36