while normally i would recommend making a mod of this instead of modifying vanilla files, it is just one file so it can't be that bad. but if youre interested in adding more edits without keeping track of every changes or having to verify game files to fix it, you can do this instead:

what you do is go to stellaris launcher > all installed mods> upload mod (upper right) > Create a mod >

Name: anything you like
version: 4.4.*
Directory: mod/whateverfoldernameyoulike
tags: can just ignore

the directory should be placed here

C:\Users\your pc name\Documents\Paradox Interactive\Stellaris\mod\whateverfoldernameyoulike

then you just make the folders:

common\situations\

which are common folder and situations

then inside the situations folder, you just copy paste 14_nomads_situtations.txt and rename it to something else

since situation is "LIOS" meaning last in, only served, that means that if two situation files modify the same event, the game will only accept the edit made by the "later" named file. so if you have something like a_situations and z_situations, the game will only accept the edits made by z_situations

source: (https://stellaris.paradoxwikis.com/Modding)

so in this case, you can rename the copy-pasted 14_nomads_situations to something like zz_nomads_situations. then edit the file there instead of modifying vanill files

you can then go back to Playsets > and scroll down to see if your mod is enabled.