The default Fire Texture show up, but now you want to make the Scripted Texture. Use the dropdown menu from this option with it's small arrow. Very important at this point yet, is to know what size you like it to have. This time you will need a source texture that will be used as base. This way you can still use the base texture as a simple texture. Both new and source textures got to have identical sizes. As far as i have tested no other Procedural texture is allowed as source texture. You will then see another window show up, the texture properties. As expected you will see exactely the same options as for any other simple texture, except that you will find some option called "ScriptedTexture". As this is all you will have to do and nothing more, there is no preview image I will show here, it would be useless. Just select your source texture and press the "Use" button in the "SriptedTexture" "SourceTexture" and that's it, just close this window and use it with the "ClientScriptedTexture" or the "ScrollingMessageTexture" from Actor browser, Actor > Info.