We've made v1.80 available as a Steam opt-in for those who wish to play with older mods for Sins: Rebellion. This is for single-player only - we will not be putting up a v1.80 ICO server for multiplayer (though you're free to use direct connect).
If you'd like to play with a 1.80 mod, select Sins in your Steam Library, right click and select Properties. From the BETAS tab, chose 180Mods from the dropdown and click OK.
You may revert back to v1.82 at any time by changing to the Default branch using the method above.