For this, and most other mods, you access their settings from the main menu, before loading into a game, under Settings > Mod Settings. For this mod, you select the weapon options you want for the Spidertron, the game will restart, and then the Spidertron will have the new weapons as its loadout when you start up a new game or load into an existing one.
This cannot be changed while the save is actually runnning (though you should be able to load into an existing game after changing the settings, and the Spidertron should change to match the new settings).
