Hi, Kelly. You might get away with oil based poly over lacquer but I sure would not want to try it the other way around. I think that there is a good chance that you will have a major peeling problem but I did not specifically research this.
I guess the first problem that I have is with why you want to do this. If you are having problems with the finish, a spray poly (if you used oil based) after sanding or a good coat or 2 of paste wax may help. You might want to check the book "Understanding Wood Finishing" by Bob Flexnor for his comments about Finishing the Finish.