Strategy for removing a bottom bracket with plastic retainers?
Based on my experience with such cups I suggest a rather robust approach:


cut off the external parts of the plastic cups with a hot knife
chisel away material from one side to expose the outer edge of the cartridge
apply penetrating oil to all areas
heat the bottom bracket with a heat gun (bear in mind the heat may damage the frame's paint @Argenti Apparatus)
drive out the bottom bracket by whacking the bottom bracket spindle with a mallet


if that doesn't work
* remove the bearings and the spindle
* uncover the other side of the bottom bracket
* drive out the cartridge with an improvised punch (eg steel tube, hex socket) and a press, apply penetrating oil and heat as before

I'm confident I should be able to remove such a bottom bracket in less than two hours now, if I must. I also shall not ever put myself in a situation where this may happen.