Question about AMD Ryzen 7 3700X

Theoretically, it is possible. However, I would absolutely not advise it, because liquid metal is meant for high-end, and the boxed cooler is not a really good cooler. It would be like fitting a VW with a V12. It would be a complete waste and totally unnecessary.

In general, I would not use a 3700x with a boxed cooler, it gets hot and noisy.

Using the boxed radiator with liquid metal is not a good idea because of the radiator's copper. I would be very careful there.........

Yes, you can use liquid metal. But keep in mind that you have to remove the already applied thermal paste from the CPU cooler first (I use cleaning solvent for this myself).