Regarding stat values I would be careful - from my own experience of testing over the last days character stats are one of the more delicate things to tweak. They range over a relatively short span in general, and the calculation in which they are used are typically relatively simple and make use of multipliers without using much decimals. So even raising stats by 1-2 points can make a huge difference - especially if applied to base stats.
Another problem I see with special stats I see is the way the code is structured - unfortunately the game makes only little use of databases when it comes to variables - instead it often applies calculation-modifying values directly in the functions - so tweaking and changing perc & Co. often includes changing a value in multiple files and lines in the code. This might be not so much a problem for sole mod-content, but modifying the core files with mod-code that is highly different in its logic and data structure could create a huge mess in the long run. But maybe that's just my layman look at this part that makes it more complicated as it actually is. ^^