Interesting question! Unfortunately I don't know the answer. I've burnished a few selfbows, but wouldn't be able to tell any difference.
I could imagine that a uneven burnish would be worse that none at all, but again this is speculative.
But burnishing shouldn't be harmful as the wood fibers aren't teared.
There's a technique to repair cracks in instruments like double basses, where you carefully hammer down a thin piece of poplar so it fits in the rift. Then soak it in thin hide glue and the poplar will expand and the crack is gone. Quite extraordinary to see!
Cons: Extra work and I doubt it changes much.