Use script to modify mesh imported from blender

I’m using Unity to plot a surface y = f(x,z). To do this, I’m using a plane prefab in the xz plane and modifying the y values of the mesh vertices according to f.
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I want a plane mesh with lots of vertices, so I made one in Blender and imported it. But Unity won’t let me modify the mesh vertices of an imported mesh. I’d like to convert the blender mesh from the .fbx to a Unity .asset file so I can modify the mesh vertices. I haven’t found guidance elsewhere.
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I’ve also tried building the plane from scratch. This works, but for some reason, my algorithm starts wrongly assigning triangles if the plane has more than 181x181 vertices, and I sometimes want more than that for functions with high curvature. So a time-tested algorithm for generating plane meshes of arbitrary vertex count would also solve my problem.
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Also curious what the proper way is to do line breaks in this forum’s version of markdown.

I needed to enable read/write in the import settings. This is found in the inspector after clicking on the blend file in the project window.

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