As stated in the other post, services run in isolation, independent of any user logged into the system. As such services cannot interact with or change user settings directly. Services are designed to provide functionality that runs independently of users. This is by design.
If you need to modify user settings then look into using Group Policies if possible. There are lots of settings that are configurable there across a single computer or entire network. GPO is applied automatically and is the preferred approach. Most browsers, including Edge and Chrome, have GPOs for their settings. Not all settings are available though so you have to look through the docs for the settings you want.
If a setting is not available in GPO but there is a registry entry to back it then you can set the registry via GPO as well. That is discussed here.
If none of that works then the final resort would be to run a scheduled task using Task Scheduler. The task can run at user startup. Note that a task has to run under a user context and if it needs admin privileges then the user account must be an admin. That account is unrelated to the user who is logged into the system. For example the auto-update tools many programs use run as scheduled tasks with admin privileges. However the limitation on this is that a task's user context only has access to their user account so you couldn't, for example, have a task run as admin for a standard user account. That doesn't make sense anyway though.