The only hardcoded list is which animation id (body ids) belong to mounts so for classic clients you have finite amount of indexes for mounts. Besides that range of 1-2048 is valid one but you have to keep in mind what is L/H/P animation type and act accordingly.
What do you mean exactly? The vague statement about issues won't help much.
Please let me know which version of UOFiddler you are using?
Do you use mul or uop file format?
Which client version files are you trying to modify/use?
Is it original client or some sort of customized format?
What is...
https://wiki.stratics.com/index.php?title=UO:Official_Communications
https://www.uoguide.com/List_of_Classic_Client_Patches
Versions depends a bit on the client line because up to version 7 there were multiple client versions. So there was Samurai empire line, gold line, AoS, ML line and...
How much you know wasn't very clear from the start. UO since beginning had a bunch of updates called expansions and some of those expansions changed map count and map dimensions. Older clients usually means everything before version 7 :) in some cases anything before 7.0.24.x which was one of...
ced+ requires proper setup for flags when dealing with uop. So you probably failed to setup the correct value of the flag.
here is archived version of the setup wiki for ced+: Главная страница - CentrEd+ - Quintessence
so for map0 I'd use prefix value of 0 and Format flag 0x1C
There is multiple ways but first you'd have to state which UOP files are you trying to unpack? Is it classic client or enchanced one? Latest version or older one?
What kind of customizations? In general muls are a bit easier to deal with as you don't have to pack them into uop. so anything between 7.0.8 and 7.0.24.1 is good enough. I don't think there is a best client version as it all depends on what you want to do.
So after version 7.0.8 or something...
This may not be possible in regular client. Besides hardcoded weather effects, regular statics and effects have limitations for bigger image sizes :) So your best bet is to code some sort of a shader in CUO or similar custom client.
land tiles
textures
and tiledata
I used just 0x0003 land tile and texture as a source but it looks like everything is as it should be.
After saving files and replacing them in uo folder and in my centred server folder all looks ok. In this case ced# was used.