Beginner ROM Hacker - Help with Underground in Platinum

[Cold Ham]

Hello. I'm attempting to make a modified version of Pokemon Platinum, and to complete the vision, being able to edit the Underground item availability would be a peach. Specifically, I want to swap the availability of the Armor and Skull fossils for the Root and Claw fossils, such that Anorith or Lileep are encountered in the main story, and Cranidos and Shieldon are moved to post game. I can't seem to find anything in the scripts of Platinum, however I'm not nearly well versed in script writing, my coding extent falls on 1 year of Java in HS, some YouTube tutorials, and pattern recognition.

Any tips, programs, or assistance would be much appreciated. Thank you in advance.