Generally speaking, your UVs shouldn't be impacted....
let's say you have a website: http://www.domain.com
All the cookies, and the ECID identification, etc would be against the root domain ".domain.com" which shouldn't care if the site is SSL or not
When you switch to: https://www.domain.com
All the cookies will still be against ".domain.com"
And even still, the ECID should be set against your organization... when I test within our network, I get the same ECID for domain.com, otherdomain.com, somethingelse.com, etc.... because all the sites are part of my organization and the user is fingerprinted as the same user across the sites... granted, I am not on an Apple, and therefore not subject to the same ITP restrictions...
But all your first party cookies should follow through from http to https with no issue