yes you can but good luck finding one
No, you typically cannot replace the wheel bearing without also replacing the hub, as they are often integrated components.
If it is 4x4 remove axle from wheel bearing assembly and then remove the wheel bearing assembly. Make sure the tone ring (looks like a ring with teeth) is still attached to the spped sensor side of the bearing, if not, replace wheel bearing assembly with an assembly that comes with the speed sensor. Replacing a speed sensor without a tone ring is pointless because it won't work.
You can change the front wheel bearings on your 2000 Buick Regal without replacing the entire hub assembly. You can change each individual wheel bearing, if you choose.
You need to remove the hub assembly and replace it. It consists of bearing, studs and speed sensor. The wires are attached to a connector which is clipped to sensor shield. You cannot remove sensor on Montana without removing the hub. The sensor is a part of assembly.
You should inspect them. They should be smooth, without pits or scores and sit reasonably in the races. If they are not you should replace them or find a garage where they would do it.
It is possible to replace the air conditioner clutch without replacing the entire compressor if you can find somewhere that sells just the clutch assembly and can get the appropriate tool to remove the pulley to get to the clutch. Try buying a repair manual and looking in there.
Turn signal lever assembly can be replaced without removing the steering wheel. See instructions at the attached link question about replacing the headlight switch on a 1999 Subaru Forester.
Yes, it is possible to replace sliding glass doors without replacing the frame by finding doors that fit the existing frame dimensions.
No, there is no repair if it it clogged. Replace it.
Yes, unless the converter is clogged there is no reason to replace it.
Yes, it is possible to replace just the toilet tank without replacing the entire toilet.
Near the bottom of the oil pan. There isn't really much point in replacing the oil pump without checking out the bearings. Get a little plastiguage and check the bearing tolerances. You can't do any good replacing the oil pump if the bearings are worn.