Can I replace a SM-G780F board with a SM-G781V board

Mateo Morales that is a really interesting question. Unless somebody has actually done this conversion, all we can offer is what the boards look like.

Here is the G780F

and here the G781V

it appears as if the mounting holes and connectors as well as dimension are pretty close (I don't want to say identical)

At this time, if the board has the right price and if it is possible to return it if it does not fit. I would at least give it a try. Let us know how it works out

As far as I know, the SM-G781V (which is the Verizon skew of the S20 FE) has some hardware differences that may prevent this swap from working properly. The Verizon S20 FE has some Ultrawide band hardware for their network, and this may cause issues when swapping motherboards, as the Verizon model is a different phone.

I would just stick to the motherboard that matches the original to be safe. It definitely is better than "saving money" when you are taking a big risk buying a board you probably can't return.