I am not sure why you would want to do such a thing, but it could probably be done using the new editors that came out with some of the patches and with SAW. The size of a hex controls range and movement rates, although you might want to change the time scale also. On a second install of the game, if you wanted a hex size of 20 meters, you would need to double the range of each weapon except some like satchel charges that would need to stay at one hex. You can use the data editor to double the range of every load. You can also use the same editor to modify the speed of any vehicles you want to include. You would use the pdt editor to change the infantry movement allowance and possibly the change in elevation per contour. It probably wouldn't take all that long to do, but I am not sure just what you would gain.
As for other mods, the best place I know of is at Task Force Echo Four. The URL is:
http://www.wargamer.com/Hosted/squadbattles/id108.htm
There are numerous mods here including the Africa at War game that uses Pacific War as a base. There's lots to take a look at including several articles on tactics.
Jeff