I am replacing the entire subfloor in an existing bathroom. The reason is that the floor is currently not level. My question has to do with the existing closet flange. I have removed the subfloor, so I have full view of everything under it now. The closet flange is connected to a 3" white PVC pipe, and there is no space showing between this flange and the sanitary tee below it. I need to replace the closet flange because it is currently too high for the intended finished floor. THE QUESTION: Can I simply cut the top part of the existing closet flange, leaving (basically) a 4 inch diameter OD and glue a 4" closet flange over it? (I went to a home center and sampled the 'fit' of a 4" closet flange over a 3" closet flange's stub... and it seems to fit very snug). Your help would be greatly appreciated. Thank You.

Well, I found the answer myself. I'll share the solution here:
Using the photo as a reference... I will cut the existing pipe exactly at the joint between the closet flange and the sanitary tee (to which that is connected). I have found that 4" PVC fits exactly over the HUB which remains (The hub end of the sanitary tee). I will glue a section of 4" PVC to this, with this pipe's length length extending it a few inches above what WILL BE the intended finished floor. Once the floor is installed, I will simply glue a closet flange (a 4x3) that is made to glue to the inside of a 4" PVC pipe. I found this closet flange at home depot. It wasn't so easy to find, since many of the closet flanges in the store were in the wrong boxes. But I found it and it fits perfectly.