For TESTNET run ./prepare.sh testnet
For MAINNET run ./prepare.sh mainnet
For REGTEST run ./prepare.sh regtest
To create a Chrome store zip for mainnet and testnet run ./makePackages.sh
Once built, you can just load the directory in Chrome extentions by enabling the developer mode.
Before making a Pull Request for WalletCrx check if what you want to modify is present in https://github.com/greenaddress/GreenAddressWebFiles - if it is then you should do the PR there.