Hi. Is it ok to cover the top of a wooden retangular framed Boori bassinet with galvanised mesh with 1cm cube openings for a newborn. The mesh is to protect the baby from cats. Thank you.

Red Nose does not recommend any products to reduce reduce the risk of a cat getting into baby’s cot/bassinet/pram while baby is sleeping, but is aware of potential risks to baby that is left alone with any animal.
Some cats have been known to jump into the bassinet or cot to be close to baby. This may risk baby’s head & face being covered.

Product Safety Australia (ACCC) develops & monitors safety standards in Australia.
While there is no safety standard for the type of product you describe, they do have information about the risk of baby getting limbs or digits stuck in small holes or gaps.
Product Safety has the following information .

• check that there are no spaces between 30 mm and 50 mm that could trap your child’s arms or legs

• check that there are no small holes or openings between 5 mm and 12 mm wide that small fingers can be caught
    in

CSS Cot safety a.indd (productsafety.gov.au)

They also recommend not altering the structure of the cot at all - I’m not sure if adding a cover like you describe would fit with this recommendation.
Never modify a new or old cot yourself, as this can destroy inbuilt safety features.

Household cots | Product Safety Australia

It may also be worth talking to your Vet about ways to make your house safe to prevent any potential risks to baby from your cats.
I also know that some people have installed a screen door on a baby’s bedroom to reduce the risk of a cat having access to baby’ in the cot or bassinet.