A - technically yes... but I wouldn't recommend it for anything other than a "trail bodge" to get you home. 415 chain rollers are 1/16th wider so the master would create a very loose link that would have a very good chance of popping the retaining clip off.
B - Generally you want to avoid more than one master link but two can be used in a pinch.
Depending on the quality or brand of chain I have often found that many 410 and 415 chains on the shelf don't even come with properly riveted links to begin with. This means that if you are capable and have the patience you could actually re-pin a link back on to a chain. It's a bit tricky to do but I have managed it with nothing more than a small brass hammer and a block of wood.