In the area where you find Groudon, there should be a script tile or a sprite with a script attached to it. Although I don't have Ruby on my PC, I can safely assume that you want to look for "setwildbattle (Groudon's # in hex) (level in hex) 0x0". You will just need to change the second hex number to a different level (still in hex). But before you compile the script and possibly mess something up, you will want to start a dynamic offset search in the first couple lines of the script. Then, the group where you change the setwildbattle command, you want to change the #org (offset) in the beginning of the section to #org @(word) and it can be any word. Keep track of what the offset was before changing it cause you'll have to change any 0x8(offset) to the @(word) same as the word before. That way, you won't ruin any bytes changed by changing the level, and all the script pointers will be changed.
Hope this helps, and before attempting this (cause I could be majorly wrong, I'm new to scripting too) always back up your current progress.
