As i understand a lot of flash files there (*fla) - was made with Adobe Flash CS4 or more - it means Adobe Flash CS6 will open it - so you can try to use it (as i understand it even have 30 day free trial time - older version had. I think CS 6 have too).
Do not think it is easy - yiu have to understand some code AS2 basics to make movies.
Learn how to animate or find animations of what you want some where, some models.
As i understand it is 2 open source projects about Peach now - and some animation in Legend Of Krystal original game.
Try to connect with people who is working with it now. May be they can tell you about some of your questions. Try to make some charecters and there animations and if they need they will add it. But may be it will be more correct to ask what do they need.
May be i am wrong but how i understand all it works:
1)There is always programmer,and humon who works with it. Some times it is hard to connect with another peoples coding stiles so it is possible to make some parts of code - but it is not simple. By the way i thing that program part was already done.
2) It always can be new animations new options new armors based on what is already done. It is easy to add in game and as i can see it adds very often
3) Animations - of charecters / enemys and etc. For example some animation that looks like some another animation by type. It is easy to add in game, with out additing code, so it is possible that it can be usefull.
If you want to make the game in different style or your own, i can tell you that it can take a lot of time so if you have bad work like for example i have now - that takes all your time and you do not have time for any thing another then sleep eat and work and may be some free 102 hours it is better do not try this way - or may be you will spend a lot of time on it. And you must want to make it very much ) So think about it =) Have you got a lot of time for it or no.
But first may be you should wright to peoples who already work with this projects
About more info your can try to look here how to make some thing in Flash CS6 - there are some tutorials
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