I also stumbled upon this issue today, where I could not save to the file due to NoSave=true.
I found on a forum post that they got their settings to save by swapping out
SaveConfig(CPF_Config, *relativePath);to
TryUpdateDefaultConfigFile(*relativePath);
I tried it as well and it works for me. But I don’t know if there are any consequences to changing it or why the previous SaveConfig no longer works.
In our case I was trying to save to ../Game/Config/DefaultCustomClass.ini
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