Is it possible to exchange the Processors from a Logic Board that has a 500MHz Processor on it with a 700MHz Processor
Hi! Unfortunately, no, it's not possible, because the processors are not plug-and-play, and are instead connected directly to the logic boards. It may be possible if you are an expert at soldering, but even then it would be a very involved and risky procedure, likely ending in the boards being destroyed and unusable.
Considering iBook G3 parts machines can be had for $20 these days, I'd go that route in order to get a faster board.