Install - existing & future users

Question

Hi there!

Im having some troubles with installing the application i have made. Its most likely down to lack of knowledge & experience so im looking for some advice as to how i can set this up.

The application has an installer and later will have some updates, the updates will be automatic using an updater application.
The application will run mostly at user level so the updates must be able to be run at this level. If IT get involved it will take weeks.
I there are some user specific registry values that need to persist per user.

Here is what i know (or at least what i think i know)

1. HKCU is a derivative of HKU. If a key is added to the SID of the active user, you will see it in HKCU
2. To add reg values to any existing user that have previously logged onto the machine, i could loop though the SIDs in HKU (excluding the built-ins) and add the reg values to each SID in Software/MyCompany,Myapp etc etc.
3. To add reg values to any future users who have not yet ever logged into this machine, i would need to REG LOAD the Default hive using C:/Users/Default/NTUSER.DAT and add the reg values in there so that a new first time use can get the values set up in the new HKU for that user

The problems i have found

1. Even as admin, i cannot see the other users SIDs in the registry. Is there something i need to be doing in order to see them?
2. i was able to load the Default hive and add the reg keys but its all ADMIN specific.

Questions
Is there an application i buy that will help me manage this? Please dont say Advanced installer, it looks great and it was expensive but there are serious limitations and i dont like sarcastic remarks when i ask them questions.
Are there any alternative ways to do this?

I did write my own regcheck class that looks for the values and adds them if not found but maybe theres a better way? i guess what im looking to do is like 100's of other application do when a new user is added to a machine. for example: i created a new user just now on my PC and logged in. I get an immediate prompt to setup my 3D connexion mouse & streamdeck. I installed streamdeck as a user but it was still installed in such a way that a new first time user has everything needed for that new user.

Thanks