It's pretty complicated depending on how the games does random battle #'s.
If this code is right, then this prevents random battles in general. 7E12DC00
If so, you need Geiger's SNES9X Debugger.
1. Load up Breath of Fire II.
2. Get into a battle.
3. Click 'Breakpoints'
4. Type in "7E12DC" in any of the lines.
5. Check 'Write'
6. Win the battle.
7. The game should stop and say that a value has been written there. If this code is the right one, that's the # for random battles.
8. Click 'Run'.
9. Click Run as many times as needed until it stops freezing the game.
10. Take the offset that it shows ($xx/xxxx) and subtract 20 from the last two digits. So if it's say, $1F/2050. It'd be $1F/2030.
11. Set the 2nd listing # to FFFFFF so you can see everything.
12. Around those you'll see what stores the values and you may have to alter code.
If you have no knowledge on ASM, I'm sure someone on here will help further. If not, I'll take a whack at it and help you out. The steps I gave you are very.. well semi vague and simplistic but if you need help, feel free to throw more questions on here.