You can read the new regulations here. The tl;dr is this (from the Atlantic):
Within the last year, several serviceman have sued the Army to be able to keep their turbans and beards. Until now, the Army has responded with temporary fixes—exemptions granted on a limited, case-by-case basis. The military expressed safety concerns about the way beards or other headwear might undermine the effectiveness of gear, and began conducting studies about the feasibility of broader exemptions.
But over time, these exemptions provided evidence that soldiers could successfully serve while wearing non-standard dress, according to Fanning’s letter. Now, officers across the military will be able to address requests for religious exemptions with the guidance of the Chaplain Corps, which is responsible for training service units on the new rules. Once an accommodation has been granted, it can only be permanently revoked by the secretary of the Army or his designee. [link]