As Mitch pointed out - Don't modify the core. The effort required to upgrade after doing that isn't going to be worth it.

As for my recommendation; Since I'm not sure exactly what you are trying to do, it's hard to say, but - I don't think there is any need to modify the core code or database tables. Since the information is only for your suite of modules, create a class[es]/table[s] to store the information and use that for the extended information.

It will keep the entire thing cleaner and simpler to maintain. Instead of re-compiling DNN to make a change, you just have to deal with your module[s]. Upgrades won't be terrible, ect.

The short version is : Don't modify the core, find a different way; You'll be happier.