I bought a second Nanohawk X because it was on sale and its my favorite quad right now.

It has a soldered-on analog VTX on top of the FC and I have a Walksnail 1S Lite staring back at me.

So would I have to remove the factory VTX or can I just solder up the digital VTX?

You're best off removing the analog VTX if you want to install a digital VTX. At the very least you would need to desolder all the power wires anyway so it wouldn't be powered on and interfering with the digital VTX, but the last thing you want on a quad that size is unnecessary redundant components making it heavier than it needs to be. So just take it out completely is my recommendation.

I believe the Nanohawk FC has two sets of post (pin headers) for connecting to the VTX board, so a little more work to remove. Also not sure if the 5v pad can provide enough current for the WS VTX which is quite power hungry. You can still try it, but if the VTX does not power up, then you would need to connect it to the 1S Vbat, and in that case you need to be careful not to fly below 3.0v or your VTX will brown out.