If modding the game into giving you more party members would create imbalance in gameplay, there will be other solutions. I just think Larian has much bigger problems than party size

Larian's Biggest Oversight, what to do about it, and My personal review of BG3 EA
"74.85% of you stood with the Tieflings, and 25.15% of you sided with Minthara. Good outweighs evil, it seems."