For future Googlers, as you say , usually looking up the transistor type gives you the datasheet, most often in PDF format, and that shows you a picture of the transistor with the pinout clearly labeled.
Example:

About lifting traces or solder pads, make sure you're using a proper wattage soldering iron (a 25W should be used for PCB work), and be very careful when desoldering (don't let the desoldering braid, if you're using that, cool and stick to the solder pad and then force it off, and don't pull on the components that are not ready to come out). If a trace does come off, you can fix it with a jumper wire (most of the time a resistor leg can be used for that), or you can scrape off some of the insulating coating from the track near the old solder pad and solder the component leg to that.

As for having the option to switch between clipping devices, my (unsolicited ) opinion is that these things are better done on things that are designed to do that and are more experimental in nature, such as a BYOC OD2 kit.

And finally, about MPSA18 vs. 2SC1815, the swap is not really worth it unless you triple the ammount of distortion your pedal can do, or you're using the pedal with very noisy single coil guitars. Even then, the difference is subtle. I'd be surprised if anyone could hear it in a live situation.

Hope this helps.