The Ethics in Government Act gave the Special Prosecutor the ability to disregard DoJ policies.
https://www.govinfo.gov/content/pkg/STATUTE-92/pdf/STATUTE-92-Pg1824.pdf
The regulations that Mueller was appointed under require him to follow DoJ policies. The most he can do is consult with the AG if he feels that following DoJ policies is not appropriate.
https://www.govinfo.gov/content/pkg/CFR-2016-title28-vol2/pdf/CFR-2016-title28-vol2-part600.pdf
(a) A Special Counsel shall comply
with the rules, regulations, procedures,
practices and policies of the Depart-
ment of Justice. He or she shall consult
with appropriate offices within the De-
partment for guidance with respect to
established practices, policies and pro-
cedures of the Department, including
ethics and security regulations and
procedures. Should the Special Counsel
conclude that the extraordinary cir-
cumstances of any particular decision
would render compliance with required
review and approval procedures by the
designated Departmental component
inappropriate, he or she may consult
directly with the Attorney General.
So Mueller could have decided there were extraordinary circumstances. Obstruction of Justice seems a pretty good circumstance dies it not? Did he consult with the AG in this matter? Did he consult with the appropriate offices?
There is nothing in the policies that prohibit him from finding that the president committed crimes.
The ethics in government act is still in effect and Mueller could have disregarded the policy.
The whole point is Mueller did not say Trump committed a crime, nor did he attempt to prosecute him for one nor did he consult with the appropriate AG offices.
He back peddled. He back peddled because he didn't have enough to make the charge. There may have been evidence, but apparently the evidence wasn't strong enough.