The Bahamut tool can mass-edit enemy data, so what you could do is x2 the EXP given.
https://forums.qhimm.com/index.php?topic=18071.0Target the game's scene.bin in FF7/DATA/BATTLE (1998 PC/7h version) or FF7/DATA/LANG-EN/BATTLE (Steam version).
As for making it into an IRO for use with 7h, the 7h Launcher has tools for doing this. Best way would be to visit the 7h site to read the documentation and/or unpack a pre-existing IRO and repurposing it into a new one with your adjusted scene.bin.
One key thing to remember with scene.bin editing; the kernel.bin (where character data is stored) also has a table of encounter IDs that the game used on PSX to load encounters faster by identifying which section of the scene.bin has the requested enemy formation. While this isn't really needed for PC, it is still used by the game and needs to be updated if the data of the game changes in such a way as to move formations into different sections. If it's wrong, then it'll load the wrong formations which leads to unintended encounters/crashes.
The Bahamut tool unfortunately doesn't do this from what I'm reading on its thread page. The Proud Clod tool, the mainline scene.bin editor. Recommended workflow is:
1) Make a backup of the game's data folder (so you have defaults to fall back on)
2) Open the scene.bin using Bahamut and make the mass edit to exp; save and close
3) Open the modified scene.bin with Proud Clod; click File then Save/Create Scene.bin. A prompt to check Kernel will appear. Confirm. If it needs to make changes, it'll tell you; confirm yes. If it doesn't need to make changes, you're good to go.
4a) If PRC didn't need to change the kernel, then just package the scene.bin into an IRO.
4b) If PRC did need to change the kernel, then by default it adjusts the one in FF7/DATA/KERNEL. If it doesn't find it, then you'll need to specify the kernel's file location. Make sure to take this modified kernel out and package it with your IRO.
Proud Clod tool is here:
https://forums.qhimm.com/index.php?topic=8481.0