The answer of that problem was to delete the "commandline.txt". Somehow this file blocks the possibility to change texture setting. Just deleted it and now it I can change settings as I want.
In meinem Hauptverzeichnis von GTAV befinden sich die normalen ScriptHook Dateien (2 Dateien), ScriptHookVDotNet (3 Dateien), ScriptHookVDotNet2 (2Dateien) und ScriptHookVDotNet3 (2 Dateien).