Credit to Zaldiir for his tutorial on how to doing this.
Donation Points system
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Come out of the Closet to everyone in the Commonwealth with a Pride flag! This mod will replace the American Flag with a Pride Flag of your choice. Your settlers will thank you. Four versions available: Gay Pride flag with Vault Boy and without. Transgender flag with Vault Girl and without.
Install with NMM, and make sure your Fallout4.ini has the appropriate edit: