Is it more worth to boymode or come out before starting my job?

I (22MtF) recently got a clinical research job in SW Virginia (very slightly blue but with a relatively large red elderly population), and applied and interviewed as a boy because I live with my parents who do not approve, and this employer does know them loosely. I will start in 2 Mondays and just got my official offer. Because I will be working with clinical trial participants from the start to finish of a study, I feel that if I am to come out, it would be best to do so before I start working with them so I don’t have to come out to them. While I’m prepared for the consequences from my parents if/when they find out, I am heavily relying on this job for entry-level experience and good recommendations. As such, I am worried that coming out with a different name, pronouns, and presentation AFTER going through the whole hiring process will be viewed as underhanded and deceitful and negatively impact the opportunity.

How frowned upon is this generally? I might be worried over nothing, as I have pretty good success with passing, especially with older people and am a terribly obvious boymoder yet they liked me anyway. I’m not terribly opposed to boymoding at work, but just don’t think I’d be good at it.