Since no one else has replied, I'll toss in my 2 cents.
With respect to the range of sight, you may be able to use a visibilty modifer and I would start there. I don't think you can modify the unit parameters, such as attack range or damage in real time during a game, but would appreciate anyone else's thougths on that.
The best workaround might be to immediately remove your unit when it enters the region and to create a second unit having the increased stats you want. I have not tried this, however, and do not know if it would be smooth and transparent to the player. Let me know if you need help with the exact triggers.