It is not, and never has been, illegal for the CDC to study gun violence. One specific part of their budget that had been earmarked for those studies was reallocated once. That's the extent of the so-called "ban" that the politicians keep harping on about.

That re-allocation did happen, but it also came with wording that effectively barred from doing any research until a recent change to the law: https://en.wikipedia.org/wiki/Dickey_Amendment