How do I blit textures onto a mesh?

I want to blit textures (like blood or paint) onto a mesh surface using it's second UV set (e.g The lightmapping UV set for a lightmapped level) similar to how you can shoot paint onto a wall or floor in Splatoon.

I've tried some decal solutions but they seem best for static situations and I need to leave splatter on the environment during runtime.

I've looked around and found people mentioning Unity's Render Texture and the CommandBuffer.blit methods but there is little information on how to use them so I really have no idea on how to proceed.

Can someone point me in the right direction? Links or tutorials or perhaps a simple explanation?

Thank you.