Is it possible to upgrade/replace built-in "contacts" aplication?

I was wondering if it is possible to build "Contacts" from ASOP/Google sources, and then replace original -single application- provided by phone manufacturer? This concerns device without root.

I assume there are three cases here:

1. Heavily modified software like for example Samsung's phones


2. Phones with modified software but heavily based on ASOP (my case)


3. Phones with pure ASOP sources (not sure, Nexus'es?)

I wanted to ask if it is correct that in case:

1. it is nearly impossible without manufacturer signing key. One can install additional application to manage contacts but most likely cannot remove manufacturer's replacement.


2. it is nearly impossible as well (same case as above) - despite application source being available, it cannot be "upgraded"/"replaced" due to fact that it is not signed by manufacturer's key


3. Only case where this might be possible ?