So, if I understand your question, you want to make your own version of Mega evolution?
Well, first things first, you should know Ruby and RGSS, this isn't the kind of thing you just jump into without knowing what you're diving in.
Now Mega evolution is basically a form change, so this Syncro evolution should have basically the same methods as the Mega Evolution ones, so a
hasSyncroForm?,
isSyncro?,
makeSyncro,
makeUnsyncro,
syncroName, and probably a modification to
megaMessage to say that the pokemon Syncro evolved instead.
Then you just need to search for all of the usages of the original method and add yours in with them.
It's a lot of work. Seriously. If you don't have a clue on where to start, practice on something smaller, because this is really big, and I know, because I tried to make
Burst Evolution when I barely knew Ruby, it was a painful failure.