HKLM in MSIX writable?

[Pollewops]

Already trying for some days, but can't make it work. Or is it not possible al all?
I have MSIX in which (in the bubble!!!) i want to set hkcu and hklm registry settings. For hkcu it is working, but hklm is not writable. What i do wrong or is this not possible at all?

I first want to know if it should be possible. If so, i can share my psflauncher and config.json config files.