Diatad said:..Is it conventional for people to switch pedals on their bikes?
Don't know exactly HOW common it is, but I do it quite often. It's really not a big deal as long as you remember that the left pedal has a reverse thread(turn clockwise to remove) and that you have the correct tool (they can be fairly tight, especially if they haven't been removed before).
Somewhere down the line one might probably argue that repeated disassembly and reassembly increases the wear on the cranks, but there'd have to be a substantial number of disassemblies before I'd consider that a real worry.
Diatad said:..Should i be saving the bike specifically for training and buy a used, 30 lb, nonliability?
I wouldn't think of it as saving, as it takes quite a lot of riding to wear a bike out. From the angle of the bike it will probably be well able to stand all your short trips and your dedicated training sessions together.
But it's always nice to have at least two bikes to choose from. If nothing else your "good bike" might be out of use for whatever reason and then your 2nd bike will at least let you get some riding in. Or equip it with racks and panniers and you'll be able to use it to run some errands with as well. Utility riding is riding too you know 🙂
Or, as others have suggested, MTB/touring shoes are OK to walk in, or there are combined platform/SPD pedals available as well.