I think this is the first time I have ever seen anyone complain about the serial number as a tell. Like, really? Anyone who knows that a certain serial number means its a rep, would also be able to tell it's a rep from all of the other more obvious tells, tells that could be noticed from way further than anyone could read the serial number.
I totally understand if a hardcore rep enthusiast or expert finds that the serial number is an issue, because they are in the game for the most gen like rep. But to say it's an issue because it's an obvious tell, is really pushing it I think.
Forgive me if I'm being presumptive, but your fixation with this and your worry of being called out probably stems from your insecurities of wearing a rep? I was like this before, obsessed with every flaw because I was worried they will give me away, but I've gradually learnt to just wear and enjoy the rep for what it is. In the immortalized words of Elsa, "let it go..."