@thestormhoover
There is, but you'll have to find the mod in your steam workshop folder and edit it in the respective file, and probably set it up as a separate mod to prevent updates resetting it back.

If you're not mod-savvy, I can give you a more in-depth guide if you need it.

I thought the idea of uncharted or no-mans space was really cool instead of the whole galaxy becoming developed, is there an option to extend duration of the empire size modifier?

Not quite. The mod only will really affect the early game as the modifiers both only last for 75 years and are expansion-centric so once the galaxy is more-or-less colonised, the modifiers won't impact much, which is why I didn't really worry about savegame compatibility - the event for it fires right at the start of the game and while it won't break anything if you add it to an existing save, it won't do anything either.

If you want, though, I could try and make it savegame compatible somehow, but I don't think it'll achieve much.

Looks awesome. Is it savegame compatible?