You can now add, remove and rotate the pipe connections on underground pipes.
As of now, there are a few missing variations so you can not have the underground part rotated on 2 and 3 way connections.
| CONTROL + R | rotate clockwise |
| CONTROL + SHIFT + R | rotate counterclockwise |
| CONTROL + A | add connection |
| CONTROL + SHIFT + A | remove connection |
As for now, rotating does not work on 2 and 3 way pipes. Rotate them first before adding more connections.
I suggest you use the elevated pipes mod too: https://mods.factorio.com/mod/elevated-pipes
I love it. :)