It might be a hard game to hack, but certainly not impossible. If you're determined to learn and put in the effort, any and every game can be hacked/modded. Here's an example of a person who's working on this game and doing great work with it so far:https://www.romhacking.net/forum/index.php?topic=30397.0
Assuming that they have the free time available, you can either try asking him or someone else at a DBZ community for help getting started. If you don't feel like taking the time to properly learn romhacking, then you could always just use something like one of the RPG Maker programs.
In that case, you're probably far better off using an engine like GameMaker and writing it from scratch instead of trying to mash new content into an uncooperative, closed-source game for a long-dead platform.
Don't the majority of people here deal with hacking and translating old games for long dead platforms? There's a reason why they're called "retro gamers". Many of these types of communities are still very much alive and kicking, such as FEUniverse (a site dedicated to Fire Emblem romhacks), among many others.
Various people wander along every so often looking to translate or mod this game (I have no idea why)
Because they're fans of the series and like these games, why else? It's for the same reason that fans of any series like games that are based on them.