Engage that in the small hole on the aluminum front case housing and unscrew the housing from the crankcase which will push the prop driver off of the shaft.
Hmmm... I've never tried this. Maybe I will next time to see how it goes. But maybe not. I'm not sure how this will affect the threads on the case and the collet.
I've always done it similar to how Dan says. I just take a couple of different steps. First, I do not use a vise. I understand that a lot of people use a vise to pushout/install the crankshaft and the driveplate, but I do not. I use a screw that fits the crankshaft, screwed all the way in so that the screw bottoms out. I also use washers between the head of the screw and the drive plate such that there is just a small gap between the screw head and the washers. After having removed the P/C and backplate as stated, I put the engine on a hard surface with a piece of 1/4" ply between the back of the case and the hard surface. I then take a small brass hammer and tap the screw head. If I've left the right amount of space between the screw head and the spacer, a couple of taps will drive the shaft down to where the screw is tight against the washers. Then I back out the screw a half turn and tap again. When I've driven the crankshaft out some, I unscrew the screw and remove a couple of washers, and start over. It takes longer this way, but at no time is there more than a small gap between the screw head and the washers. If the gap is too large, tapping the screw could cause it to bend instead of driving straight down. Going slow and easy ensures I don't mess up anything. Been doing it that way for as long as I can remember working on these Cox engines. But I'm just a layman. Maybe Larry will eventually show up and give the "official" recommendation.
As for parts, I've ordered from both Bernie at Cox International, and Matt at EX engines. Both have excellent parts and service, and you can't go wrong with either. I tend to use Cox International more, but that's just an irrational preference.
For fuel, the guys at the local field use 10-15% mostly in their Cox .049 and .09 engines, but I think that's more due to availability than anything else. The .049's run on 10%, but I don't think the engine is particularly happy with that. The .09's are less finicky with the 10%. A .15 should be even less so. At least, I hope so, as I plan on using 10% on my Medallion .15 when I take the Akromaster out to fly. The larger engine drinks too much fuel to use the expensive 35%. I, personally, use 25% or 35% on my small Cox engines. If I run out, I use some doctored fuel that I have at 20% until I can source some more. All castor would be great (especially for the smell), but half and half should be perfectly okay. I once did an unscientific test where I took a brand new engine and ran a gallon of half and half through it, then tore the engine down to see if there were any adverse results. That was when Hobbico came out with their new half and half Cox Superfuel a few years ago.
Sorry to ramble on so much. Hope you got something out of this. Again, this is just what I do. I'm no expert here.
Mark