How do I upgrade my Cycle Poco's lens?

Currently I have a Cycle Poco No. 1 I bought a couple years ago. I've been wanting to get a copal lens for it but I'm not sure it's even possible. My lens board is around 50X50mm with a 35.7mm hole in diameter. Will buying a copal 0 and trimming the lens board down to fit be okay? I don't want to buy a new body because I'm pretty happy with the one I have.

There are no “Copal lenses”. Copal is a shutter. Nikon, Fuji, Rodenstock, Schneider, among other lens makers, mounted their lenses into Copal, as well as other brand shutters.

The standard hole for a Copal #0 mounted using a retaining ring with a centering ridge is 34.6 mm in diameter. So until you tighten the retaining ring the shutter will slide around a little in the hole. This can be lived with since once the retaining ring has been tightened the shutter won't move.

I just measured a Copal #0's outer diameter. 61.35 mm. Make a 62 mm paper disk, lay it on your camera's lens board and see what it interferes with.

There's no guarantee that a Compur, Prontor or Seiko #0 will have the same o/d as a Copal #0. The #0 standard specifies tube length and threading, and that's all.

Your camera should have a removable lens board. Remove the lens board with existing shutter/lens combo. Measure the diameter of the bellows opening, this is the maximum diameter of the lens rear cell that will fit onto your camera.
Measure the lens board length, width, thickness, and any notches on the back side of the lens board.
Make a new lens board with the same dimension as the original but do not drill a hole for the shutter.
Find a lens whose focal length suits you, rear cell fits into the front of your camera then drill a mount hole for the shutter to mount in.
Make photographs with the new to you lens.