So your organisation has a non-employee installing software on company machines. IMHO not a good situation.

At the very least you can organise a meeting with your manager, the manager you have in common with the system administrator, and the system administrator and put your case across (in a very calm and dignified manner!). A major aspect of this should be governance and separation of responsibilities.

It is part of the job of technicians to advise managers, and for managers to make the final decisions and take responsibility for them. If your managers say the way things have been done is the way they want it done in the future, your position is clear. You can then decide if your career is best served by staying in place or getting a different job.