What texture and other modifications are still in use/allowed?

[AbstractVision]

When I played on p99 a few years ago I was able to use luclin character models, higher resolution world textures, luclin era? armor textures, new(er?) spell particles, higher quality music files, custom loading screens, and custom UIs.

Now it appears I can only use my custom UI and load screen. When I try to log in with any of the other things I get a spells files outdated or error message. All the threads about the previously mentioned things are either locked or deleted/missing. Many "official" links like the one in the sticky of technical discussion for newer character models just lead to a non-existent page.

I found something in reference to a bug that was being exploited in a post somewhere on another forum about transparent wall textures and thats why you can no longer change texture files?

Does anyone have any clear information on why I cannot use any of the above mentioned textures/files? Are there any legit mods I may use to modernize the look/feel of the game a little?