Would it be possible to switch out the board and electronics in a legacy hilt?

I mean, technically everything is possible with enough time and/or money. But it would absolutely not be easy or something we’d recommend. Just getting the sabers open alone is a ridiculous feat, and seem to not be possible in a non-destructive way. These can’t simply be unscrewed and swapped–There’s blood, sweat, and minor skin burns involved, and that’s not even getting into whether or not you want to keep the existing blade connector, RFID crystal scanning, or any of the existing features.

Here’s a video example of what it takes to take a part a legacy saber: Kylo Legacy Saber Teardown