Mackintosh, the captain of the side for the past two years, plays the same position - loosehead prop - as the new signing, 88-test All Black Tony Woodcock.
That might suggest Mackintosh's days are numbered but Joseph said all the props were vital for the franchise.
Woodcock, Mackintosh, Chris King and Ma'afu Fia have all signed to play for the Highlanders next year.
Joseph said new rules, which were 90% likely to be introduced, would force teams to have two props on the bench. This would eliminate the need for a utility prop in the reserves and mean all four props would be needed for the franchise every week.
As for the captaincy, Joseph said he had not even considered that issue as Woodcock had only just signed.
He said he was pleased to get a player of Woodcock's standing.
"He is the most capped prop this country has ever had, and comes with all that experience," Joseph said.
He said a player like Woodcock sometimes needs to be mentally freshened up as well as being physically fresh and he used Brad Thorn as an example of a player who did that and achieved great things.
Prop Ben Franks was another player the Highlanders were hunting but Joseph said Franks had yet to make a decision.
Franks was believed to be deciding between the Highlanders and the Hurricanes and was favouring a move to the capital.
