How do I change the fuel pump?

There may be an access panel built into the underbody panels, either under the rear seat cushion or slightly further back in the forward trunk area. That is exactly what they are used for: to get to the fuel pump module assembly without dropping the tank. Under any padding or carpeting, a little round metal plate with screws holding it on. A lot of Buicks of those years had the access plates, a lot of cool imports have had them for years, maybe stop in and ask your friendly Cadillac service technician if your car is so equipped. It is a real time saver, so easy that every owner could do it themselves. Just like changing a fuel filter in the gas tank of your lawn mower, it's almost that easy, compared to dropping the gas tank, now that is a real job, only outgoing optimists should try. I'm retired now from such endeavors, that's all a pleasant (?)memory, but I have sure contributed a lot of vocal outpourings against rust. and the worse the frustration gets, the louder the venting. Alas, why is cursing so common and quick to thought? It took me years to understand timelessness. Yeah, that's it, take your time if you have to drop the tank, it's really not that hard a job, not like rocket science where a bolt takes days to conceptualize, a nice afternoon enjoying the late sun while you change out a ***** fuel pump.