Um...yeah...a while ago. I did it to change the map sizes to all Felucca sized. I found someone else's posting in the RunUO forum about how to do this and where to look in the executable. The versions were different but I still found the maps.
What do you need to know? Not an expert on the subject...but I've done my share of hexediting.
There is a tutorial on how to hexedit the client to do this. In fact you can do this to create much larger maps too, with no real impact on client performance, I tested it out once.
If you do go for a larger or non-standard sized map, remember that you will need to edit the boat system to allow boats to cross to the other side of the map. And if any land areas go across the wrap points you'll have to figure out a way to get the player from one side of the map to the other.
Note: Ryandor.com isn't very active these days but it's still a valuable resource for world building info!
Thanks HellRazor.
It took me a little time tracking down the link and then ServUO was down for a bit.
Here's a screenshot...I don't think it was the one (now missing) from the original thread. I think this was my own screen shot so I remembered how to do it....though I thought I had all 6 highlighted....oh well.