1 – Go to the \ Documents \ Paradox Interactive \ Stellaris \ folder
2 – create a “common” folder if it does not exist
3 – in the “common” folder, create a “subjects” folder
4 – Go to the folder with the installed game (for the license – steamapps \ common \ Stellaris \ common \ subjects)
5 – Copy the 00_subjects.txt file from there and paste it into the “subjects” folder that we created
6 – Open the file 00_subjects.txt and add ‘can_be_integrated = yes’ in the lines for the protectorate. It should look like this:
protectorate = {
can_col yes
can_be_integrated = yes
7 – Save file.
After this protectorate can be integrated as a vassal.
But personally, I like that protectorates exist, in my game they cannot catch up with me in terms of technology or catch up for too long, so I also changed the trigger threshold when the protectorate becomes a vassal, of course it depends on which empire is in size, in my empire it was with one system (there is little sense from them and I wanted to integrate them as soon as possible) and I set the threshold to 0.3. After that, protectorates became vassals faster. For example, these are the last lines in this file:
become_vassal = {
tech_unlocked_ratio = {
who = from
ratio> 0.3