Tip replacement
I replace my own tips and have been doing it for more than a couple of decades.
I use Locktite Gel Super Glue and it works well. I uses to use Tweetens tip glue, but it takes a long time to set up and I noticed more tips coming off as compared to the super glue. Just be careful, because if you get it on the side of the ferrule , forget truing to get it off (acetone might work...as I expect nail polish remover might work as well).
I have a tool that I bought to make sure the ferrule was flat. It clamps to the shaft. There is a flat/disk that you use to make sure the face of the ferrule is flat. I can't really describe it well...here is an image;
http://www.pooldawg.com/product/cue-top-sander-machine
I don't do anything fancy for lining up the tip. I put a piece of tape around the ferrule to protect it and then tape a square piece of paper on the end of the shaft. When you put the new tip in place, wrap the paper around the new tip and ferrule...it will do a pretty good job of centering the tip.
For cutting the tip down, I use a dremel tool with the small drum sander attachment. You have to be very careful here, as you can easily damage your ferrule. I just take my time and am very careful to not move the sanding part below the the tip onto the ferrule...this sounds more difficult than it is. A lathe would probably be easier and do a better job...but I don't have one at the moment.
When I am close, I sand by hand (again, I protect the ferrule with tape...and don't sand through the tape). When it is done, I burnish the sides of the tip and shape it. For sanding by hand, the rolls of plumbers sandpaper (used to prep copper pipe before soldering) works well.
Is this something i would recommend for just anyone to replace their tips...no...too much possibility of damaging the ferrule...but i've been doing it this way for almost 30 years. As someone else said, it is better and easier to find someone who does this...but if you are a do it yourself kind of person...this way will work and give you decent results.
John