I FINALLY GOT IT TO WORK... but then I had to stop playing for the day.
BEHOLD: PARTY OF 6!!! TAV + ALL ORIGIN CHARACTERS
So, first you have to use the ExtratTool-v1.15.10 as instructed in the Mod instructions. Switch Max Party Size from 4 to 6 or 8. Save. I even used the Extract function and chose the same file folder as the Save I was using. Not sure that's necessary, but I did it anyway.
But here was the step that I had to do to make it work in the end. I loaded up the modified save file, and they still wouldn't let me add more than a party of 4. So I dismissed everyone from the party and reinvited everyone back into the party. THAT'S what made it work. Once I reinvited everyone, suddenly, on the 5th person, VIOLA! No more, "You're full up."
Now I just need to test combat with it. Looks like I'll be starting over my 4 Custom Character game to try it out... or I may just keep going with Tav and the gang! Yeah. I think I'll do that. Then I don't have to dismiss or pull in any characters at all for story content.
Ah! This is great! I can't wait!
congrats! that's really cool. while i still do not have any urgency in reinstalling bg3 (i only completed bg3 EA once during the first EA initially released), are there mods to tweak enemies stats? that will be a great start to be very honest. i'm really looking forward on the release date of this game and really wanted to play with 6 party characters. but encounter balance are still important especially with their restored dnd5e stats.