I don't know anything about hacking Ogre Battle for SNES, but WinHex32 is a great Hex Editor. It has some features just for SNES roms. I suggest you give it a try. Hex Workshop and Thingy32 are some other common Hex Editors.

I'd recommend Windhex. Though I seem to recall that some (major) parts of Ogre Battles text are compressed.

Also, most hex editors work on every format. They only display binary data after all.

Is there a way to tell, from looking at it, whether or not the text is compressed? I've tried opening the Orge Battle ROM; what I see for the most part are a series of "F"s and "0"s, and some other text as well. Does this mean that nothing in the ROM can be edited?

Sometimes you can see a trace of partial words or a single word or two. Typically if you take the first word of the beginning of a block of text (say the very first word in the game) you can still find it via relative searching. That's because every compressed stream starts with a few uncompressed characters. Then, you'd see the first word or two (or just a few characters) and the rest garbled. you're obvious out of luck if the strings aren't in order because you'll have no idea what is the first word in a block of text. Your millage will vary depending on the game, the compression scheme, and how it's set up. If the game used dictionary or DCE (dual character encoding), in addition to a real compression method, chances are you won't see anything at all.

Aside from instaces like that, no, you can't really see compression. But if you have scanned the ROM and see no text, have tried relative searching a few times and come up empty handed, chances are it's compressed. That's typically how you might know. This is where you may want to jump into learning to use a debugger and some assembly. Rather than playing the trial and error game, you can know for sure from the game's code. But that's a whole new challenge in itself.

ROMhacking is time consuming hard work! 

I can tell you with absolute certainty Ogra Battle CAN be modified.

Here, this is my favorite starter document on compression. See the LZ77 section. That's basically LZSS.

http://www.romhacking.net/docs/114/

You need basic binary hex knowledge though to understand any compression. All compression is, is eliminating the redundancy in data.

As a newbie, you've got a long road ahead. Don't be discouraged, but it's going to take you quite sometime to be able to handle Ogre Battle, but  it can be done.

Well, compressed blocks usually have large differences from one byte to the next.

...You're right about that, considering I understood about 3% of what you went into. All I'm looking to do right now is open up the game I've been playing for a decade and figure out how to change the first line of dialogue into something else. Then the second, and so forth. I know it's not going to be easy, though.