Do I have to replace the cable housings when I replace the cables.-Not unless they are in bad shape
Even if I retain the same cable housings, do I need to retape the bars as part of this process- maybe, it depends on how well the old tape holds the housing in place when you take the old cables out. If you can thread the new cables through the housing without removing the tape then you will not need to replace the tape.
How do I know when I need to replace the cables- When they break or get rusty or start to stick on shifting. Usually cables stretch a bit over time, you don't need to replace them, just tighten the cable at the derailleur.
How do I know what type of cable / cable housings I need to get. I have 6700-All shift cable should work on any derailleur as they all use the same type of end at the shift lever. Some sstems need compressionless housing though.
What tools do I need- allen wrenches that fit the cable clamp on the derailleur, and if your shifter needs allens. You will also need wire cutters. It's all pretty easy
Here is how I would approach replacing the cables.
-Switch into your smallest front cog and your smallest rear cog to release all tension on the cables.
-Next undo the clamp at the derailleur end and snip off the cable at that end so that the bent cable from the clamp is off-it will scratch housing liner when you try to pull it through if you leave it on.
-Push the cable backwards through the housing and you will see where it comes out of the shift lever. Pay attention to the routing at you remove the old cable.
-Thread the new cable while matching the routing of the old cable. If you are lucky you can just run the new cable through the lever and it should hit the housing hole that the old cable just came out of. Just keep pushing the new cable through until it pops out the other side of the routing.
- make sure that you route the cable the same way the old one came out and then make sure the cable is snug, but not tight on the derailleur when you tighten the clamp. In the samllest cogs the derailleur should be in the relaxed position without the cable pulling the mechanism.
-Turn your bike upside down and turn the pedals while cycling through the gears to make sure it is hitting right. Adjust the cable tension until it operates smoothly.
Because you are not replacing the derailleurs you should not need to mess with the set screws at all. Only mes with the cable calmp screw on the derailleurs.