Old version of guixt.ini still active: I work with a local guixt.ini file in C:\Program Files (x86)\SAP\FrontEnd\SAPgui. But instead of the version that I stored there, an older guixt.ini with different script directories becomes active. What could be the reason?

This is probably due to the "VirtualStore" concept in Windows, introduced by Microsoft with Windows Vista. When a program without administrator rights tries to save a file into the programs folder, Windows stores it in C:\Users\USERNAME\AppData\Local\VirtualStore  and will also read the file from there later on. Solution: Display the SAP GUI programs directory in Windows Explorer. In the explorer menu bar you will see a tab "compatibility files"; double-click it to navigate to the virtual store folder and then delete the guixt.ini file in the VirtualStore