Chinese languages

I was wondering if anyone could tell me how to say the following as a chengyu?

You change the external wrapping, but the contents are still stay the same, ie. superficial/meaningless change? Or something to that effect (there are a lot of ways you can express that sort of meaning in English).

I'd appreciate any help! Thanks

it means '去其糟粕 ，留其精华' (qu qi zao po liu qi jing hua ）in chinese