Leave it. I have done the sump gasket a couple of times with my 3T and yes they do squish out at the sides bit. I also used a bead of silicone between the sump and the gasket just to be sure but if I were you I would just run it and see how you go.
I have never actually changed a gasket when the motor was out, only in situ so yes it can be done. Undo the passenger side mount, jack up that side of the engine, undo sump bolts and then carefully manouver the sump past the oil pickup and job done. The fact that I have done it a couple of times means it took me maybe 20-30 mins to do the whole job.
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