A mod that removes the (client side!) check for experimental planets from the planet selection. With this you can select any template you want and host it. I am not 100% how the server reacts to certain planets. Tests I made: -Lava and Metal can be hosted on a custom template basis with this -A Size 100 template results in a size 65 planet ingame. Dunno if it was a random bug or if the server caps the size. So basically you can play lava and metal on custom planets with this, about other limitations I don't know for sure. http://www.nanodesu.info/stuff/pa/mods/unlimited_templates.zip Install it the usual way, recommended is the ui mod manager.
My guess is that lava planets and Metal planets (by themselves) are accidentally labelled experimental and blocked on the client side, which this mod fixes, whereas the planet size and water height are still capped on the backend (above 65 planet size is considered 'experimental', as is above 60 water height).