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I wouldn't be concerned about them cracking from the extra pressure, from my own observations (not an engineer) the metal sleeve will not "hold" the bushing in position, it acts as a smooth surface that the replacement urethane bushing may slide or move in.
without that sleave, some of the urethane bushing would be sticking out the front surface of the beam , some would be out the back. this would keep it from moving in the beam. IMHO that is the reason for removing the steel sleeve, this way the job isn't getting done twice when the bushing pops out.
I've never worked in a flat rate shop but this would be a free comeback/installation failure by tech.
I've been in the trade too long to respect automotive engineers .