The oil pan can be easily removed with the engine in the car, clean working conditions and working on your back may be an issue trying to replace the bearings though. I imagine with the right amount of determination and small fingers it would be possible.
An important note, the Oil level sensor on the front of the pan has clearance issues with the oil sump tube when dropping and installing the pan. Unscrew the sensor and let it set loose through the hole and it will make life much easier. I broke one the first time. through.
The problem with picking and replacing parts is that if one part has excessive wear, it is likely that other parts have excessive wear also. Main bearings, balance shaft bearings, rings, valve guides... it is a game of luck at best. The overall condition and mileage of the car should help decide what to do. If the car is very solid otherwise a rebuild or low mileage salvage may be a reasonable option. If there are other looming issues, Chassis rust, suspension issues, body corrosion, transmission problems, limping by on heavy weight oil and additives may be the way to go while saving for a new vehicle.
To my brother I recommended nursing the old one along and saving for a replacement car. He disagreed as he does not have much money and really likes this car. It has a considerable amount of under body rust but is in excellent shape on top. I've already replaced most of the suspension, portions of the brake and fuel lines, fuel pump, wheel bearings, and brake calipers.
We were fortunate to find a 51,000 mile car fax verified motor and transmission pair for $1000.00 less than an hour away. Finding this was very fortunate as a direct swap needed to be from an H body 96-99 vehicle. There are two possible final drive ratios also further complicating matters, a 2.84 and 3.06. Engines from W body and later model Bonneville'* will work but they require some electronics and parts swaps.