Yes it’s possible, but not easy to screw up and the card in question does in fact have a dual BIOS switch
I flashed my 5700 Red Dragon to a 5700XT Red Dragon...also with a dual BIOS. I do agree it was very easy and I also wouldn't say it's NOT easy to screw up. All you need is a power fluctuation during the flash so that's where a dual BIOS is going to save a lot of grief if it happens.
Once flashed, you also have to remember there was probably a reason your GPU was binned down to a 5700 vs. being sold as 5700XT. I have to drive with higher voltage for similar clocks, for instance, and so it runs hotter. Some might be different and only got binned down for market segmentation, if so I wasn't so lucky. But even getting only 1924Mhz at 1105V gives me a nice uptick allowing 1440P very high to ultra settings like a real XT.
And a last, general rule for Navi is that opting for lower voltage over higher clocks is better for a smoother FPS and game play.