Former High Court judge Virginia Bell delivered her review on Friday determining how and why the action was taken by Scott Morrison and who knew about it.

Home Affairs Department secretary Mike Pezzullo shared with the judge he would have been placed in a "position of untenable conflict" had the former prime minister and former home affairs minister Karen Andrews given him contradictory orders.

Ms Bell's report revealed Mr Pezzullo and fellow secretaries, of which Mr Morrison assumed power over, had been made aware of the changes until it was publicly revealed in August this year.

"Mr Pezzullo observed that he would have been confronted by two cabinet ministers, each authorised to administer his department, exercising power inconsistently over the same subject matter," the report said.

"Mr Pezzullo considered that he would have been placed in a position of untenable conflict given that Mr Morrison, in his capacity as minister administering the Department of Home Affairs, would not have possessed any greater authority than his fellow cabinet minister, Ms Andrews."

Former home affairs minister Karen Andrews said she was not aware she jointly held the portfolio with her leader.

Mr Morrison also appointed himself minister of the departments of health, finance, industry, science, energy and resources, and treasury without the knowledge of the appointed ministers.

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Earlier on Friday morning, before the report's publication, Mr Pezzullo spoke to public servants about the importance of responsible government.

In his speech, which delved into the history of structure and responsibility across the British and Australian systems of government, he argued for more flexibility across government hierarchies.

But the top official added "vertical responsibility still matters" while steering clear of the former prime minister's much-criticised actions.

"I certainly have no intention of straying anywhere near the inquiry that is being conducted by Virginia Bell into the appointment of the former prime minister to administer multiple departments - whose scheduled date of reporting was not known to me when I agreed to give this address on this day," he said on Friday morning.

"Parliament still has to be able to ascertain which minister is hierarchically responsible in overall terms for each department, agency and other body, for instance in relation to resourcing, leadership, management, workforce, performance, and so on."

Former treasurer, and personal friend of Mr Morrison, Josh Frydenberg, said he felt "angry, hurt, confused, dumbstruck" after finding out via social media the former prime minister secretly swore himself into his portfolio.

Mr Frydenberg told author and Nine newspapers columnist Niki Savva his former leader still hadn't apologised for his actions, calling it an "extreme overreach".

"I don't think there was any reason for Scott to take on the additional Treasury portfolio," he told Ms Savva, according to an extract from her upcoming book on the Morrison regime.

Morrison participated in the review undertaken by the former judge through a legal representative.

Deputy opposition leader Sussan Ley said the Coalition's shadow cabinet would support any recommendations outlined in Ms Bell's report.

Ms Ley would not comment on the snub, saying it was a decision for the Member for Cook.

"What people do with respect to inquiries is up to them," she said on Friday morning.

- with AAP