I can't really point you toward a guide, other than the wiki, but start-system modding is actually pretty easy. If you've managed save-file editing, a custom start system should not be much of a challenge.

The Youtube tutorials from launch are pretty old, but should still work to an extent.

ouch..
I can edit the savefiles to make custom solar systems but idk how to make that as a mod sadly..
At least u know any site or guide i can read to understand how to turn a savefile spawning system into a mod?

Thank you, but I am not taking requests at this time.

Can i request you a starting system mod?
I sended a friend request to talk.
Or tell me where i can request you a mod if u dont want accept friend request from strangers, np.

Could you make the Ketling system start? (ruinous core, etc)

Hey can you make this spawn next to Sol?

It'd be really cool if this automatically spawned close to Sol as Sirius, Procyon, Barnard's star and Alpha Centauri do. The cool thing about TRAPPIST-1 isn't just the ton of water worlds (the ones in the habitable zone are apparently mostly ocean!), it's also that at 40 light years away, we have a snowball's chance to get there ;D

maybe adding at the end of sol system settings in prescripted_species_system.txt :

# Sol Neighbor Tier 3
sol_neighbor_t3 = {
name = "Trappist-1"
class = sc_m

planet = {
name = "Trappist-1"
count = 1
class = star
orbit_distance = 0
orbit_angle = 1
size = 30
has_ring = no
}

planet = { ...

Or something similar after you correct it fixes it, since yo can force a system to apear only once and if somebody choose sol system as start the game will start creating the galaxy from the sol system and neighbours it probably not appear a second time as a regular star system

Nice, now there is only one, i check, but it's random located even if the player start on a sol system.
Since i was so lucky talking you about that issue i'm going to the paradox forum to request the release utopia on monday, wish me luck XD.

@jcgcotillo- turns out, there is a setting to force a system to only apear once- and I overlooked setting it. It should be fixed now :)

@- Aparently, I need to turn down the spawn chance. A lot. Thanks for the heads-up! :)

choosing sol system as start system i already find 4 Trappist-1 equal systems, in the other hand, thanks for the work, i wish you continue developing it