Due to how the mod works - it is not possible to launch rockets.

Single line I've tried using should fix this since the silo uses a fixed recipe:
data.raw.["rocket-silo"]["rocket-silo"].fixed_quality = "legendary"

So far it has worked, but haven't yet tried to send a rocket.

Yep. This works. Easy fix for anyone that wants to use it until it's updated.
Edit the data-final-fixes.lua to include:
data.raw["rocket-silo"]["rocket-silo"].fixed_quality = "legendary"
Then it will set all the ingredients to also require legendary.

New issue however - Can't used quality Space Platform Foundation as actual space platform foundation