Can I replace an under mount sink with a drop in sink without replacing the countertop?
I have replaced bathroom sinks of various types with ceramic style sinks that sit from the top of the vanity cabinet surface.
This work best if the before and after sinks both had the faucet holes as part of the sink body itself. Another factor to consider is selecting a new sink that will work within the hole size of the old sink. This can make the replacement job tremendously easier, particularly if the existing vanity has a tile top.
I have found that you should be prepared to fully replace the drain down pipe, p-trap and drain line to the wall. Differences in sink dimensions and basin depth will likely leave it difficult to fit the old stuff to the new sink. Besides the new parts are not that expensive and it is far more pleasant to fit up clean new parts.