How to modify allocation percentage for all the resource of a team without entering single user profile?

Adding a member into a project area means allocate it to all the timeline of each team area he participates in and in the project area: i.e. if a member is associated to a project area and to 3 team areas inside the project area, it is allocated by default for a 25% to each timeline (the one of the project area and the ones inherited by the team areas).
Is there a way to avoid this? It is possible to assign the new member only to the project area's time line?
Again, is there a way to modify massively the allocations already made for all the members of a given project?

Thanks