It's a big undertaking if you try it on that scale. The older clients have fewer empty spots so you wouldn't have enough room to add everything from the latest client. Movable multis (like boats) would be beyond anything I've tried. I inserted new artwork and mobiles into 7.0.7.1 for the Whispering Pines shard but it's still running RunUO. In fact, it's so old (RC1) that it couldn't run this client without many edits to the core, but I made it work! I also replaced the Fel map with a Darkshard map which took some doing. The game designers never considered that Tram and Fel would ever be two different maps. I'm sure 7.0.7.1 isn't the final MUL-based client but it's close. It'll give you TerMur support but not High Seas or later content.
I'm tinkering with my own shard now and I decided to pass on the customs this time. It was a tough choice but there is so much more to work with here that I don't feel like it's a limitation anymore. There are plenty of good shards already that work hard on staying with the current release so I've decided to pick one "moment" and really polish it instead. Even without custom art and mobiles I'm tinkering with dropping in the UOP files from later clients so I can have the newer items to work with without having to adopt the major changes in the client and its gameplay.
