sudo ./install.sh needs internet access to install.
If you edit the install.sh script where it downloads the configuration files edit them and install ppp.
You can store the files that are downloaded and change the script according to it.
Once you have installed ppp before, you will not need to re-install it. You can comment out the installing line (line 79 at the moment).
If you have already everything installed… then changing the APN from /etc/ppp/peers/provider is enough.