Are there any recommendations with how to store the deadname of a contact that is undergoing a gender change? i.e. They have not yet changed their legal first name and we want to communicate with them using their (corrected) first name, but legal/financial documents must use their deadname.
A custom field works well, but I would also consider repurposing the nickname field via Word Replacements, since you can enable QuickSearch on nickname.
With regard to legal/financial documents, I'd probably repurpose the postal and email greetings for normal communications and communications requiring the deadname. If you're already using those, you could also create a deadname salutation using the Salutations extension.