How do i vertex paint on bsp brush?

Hey can anybody help give me some insight to a problem that ive been experiencing. ive designed a basic level design of a underground bunker for a game me and my friends are working on. Ive built the basic level design using BSP brushes. Ive added materials to all of our rooms to get a basic idea of how we want the materials layed out. Im currently trying to learn vertex painting to create more advanced realistic materials. but when I try to use the paint tool on the brushes it doesn’t show any fallout brush for me to actually paint anything. I realized I needed more vertices on the brush in order for vertex painting to work. How do I add more vertices to a brush so that I can vertex paint it? Im starting to worry that you cant vertex paint on a bsp brush. That would suck because ive spent days designing a level design and placing materials to our level. Plzz somebody tell me they do it all the time and that its easy, end my suffering lol. Thank you!

lol, you cant vertex paint bsp.
You could convert the brush to a static mesh, but thats highly unoptimal.
you’d need blender, 3dsmax, maya or modo (to name a few) and create meshes in that software.
Can even pre=paint the vertices in those 3d tools.