Help understanding GEN3 rom hacking. Specifically edit things not accessible with PPRE

[SDG_Ryo]

Hey!

So I am trying to learn how to make a ROM hack and would love to edit what Pokemon I can encounter when and what they evolve into.
So far, I managed to change evolutions (using PPRE), encounter tabled (PPRE), starters (UPR) and gifted Pokemon (PPRE script editor). I now want to complete the rom hack but can't really find where to edit things like:
 

1. What fossils I get
2. in-game trades
3. tree encounters

I found some of the files that might contain the information that I need (.narc files), but can't find a way to open/edit them. I have a programming background in C# so I do understand coding, but am missing some pointers as to where to start.

Thanks for everyone that can help me out here! I will credit you in my work!