Remodelling the top of a soil pipe

I have a plastic soil pipe that comes up through the floor into an ensuite bathroom (see image below) and I want to change the angle at which the toilet waste line enters the stack and adjust the other smaller waste inflow pipes. Currently all the stack above floor level is made up of couplings and fittings and the vent on top. There is no plain pipe accessible. The couplings are all glued together.

So the question is, if I am careful is it likely that I can cut through the lowest fitting and peel off the remaining collar that is on the top of the actual pipe. I appreciate that removing the part of the fitting that is left on the top of the pipe will not be easy but has it been done?

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You could try but it wouldn't be smooth enough for new fitting to seal.

I would cut below ceiling and fit a straight coupler and new pipe piece then you can put anything you want on top.

Daniel.