Not if you want them to seal, no. Assuming there was any reason to replace them in the first place, the faces new valves will be perfectly concentric with the stems, perfectly round, and ground at a perfectly flat 45 degree angle. None of this will be true of the used, worn seat, so how do you expect the valve to seal against compression and combustion?
can you not install new valves with out re cutting seats ... ?
Cutting the seats is imperative in order to get them to seal, and correctly finishing them is critical to making the valves last as long as they should.
Which brings me to the question: How is your cranking compression, anyway?