Gamerules/config options to control the following would be really helpful:

• Disable assimilation spreading altogether, so we don't have to disable random ticking entirely to pause the spread
• General spread chance per tick, as well as
  • Tentacle spread chance
  • Gore spread chance
  • Sculk spread chance
• Spaceships:
  • Spawning enable/disable
  • Crash destroys blocks
  • Crash radius
• Sculk tweaks:
  • Sensor spawn rate
  • Shrieker spawn rate
  • Catalyst spawn rate
  • Spread range
  • Shrieker bramble range

These are good ideas! I'll keep this issue open for now since currently I'm not actively working on the mod but I definitely would like to add some of these for the next update.

The starship can already be disabled in the released version, though unintuitively it's in the "events" config since more invasion events were planned.