[plt-scheme] Resetting the PLT_EXTENSION_LIB_PATHS variable doesn't work

Hi All,

I'm trying to reset the PLT_EXTENSION_LIB_PATHS environment
variable in my pre-installer for sqlid. However, it doesn't work, because
somehow, in module 'setup-extension', the environment variable is read
only once.

Is there a way around this?

Thanks in advance for your answers,

Hans