You have to install the Polygon Panel SIP Patch for it to show up in SIP

Cool! This really speeds up the building of interior, rather than to pick it every time with WEdit. Although, I can't find Polygon Panel anywhere in Spawnable Items, I can only get it via /spawnitem or the remains of WEdit filling iterations.

Thank you for not swamping the c menu with bullshit.

It might be worth noting that you can enter vanilla servers with this mod installed just fine, and that the block visually becomes a perfectly generic item when you hold it near a player that doesn't have this mod installed, and becomes an actual perfectly generic item if picked by a player without the mod. Also, crafting the block inside multiplayer doesn't appear to cause issues either.
All tests done in a local network between the Steam version with the mod installed and the GOG version with no mods installed at all.

:3

Absolute madlad.