What can a tenant do if the property manager enters the apartment without any prior notification?

Unless a window broke and this was a genuine emergency, your property manager should have given you advanced written notice, or made an appointment with you.

You're right ot feel invaded. Hopefully the property manager has apologized and knows not to do it again. You may want to send a copy if your letter (sent by certified mail or Fed-Ex so you can prove receipt) to the owner of the property, and to the property manager's supervisor, to advise them of this violation.

If you haven't already, you may also want to check your written tenancy agreement to see what if anything it says about the landlord's right of entry, so you can include that in your cease and desist letter.

It sounds like you have no damages at this point, and you were lucky to come home to be present for at least part of the window replacement so you could supervise it. It seems unlikely that the property manager and 2 window installers would do anything improper in each others' presence while doing this, but you may want to put a "security freeze" on your credit (please see the link below) just in case.

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.