Regarding setting parameters:
Launching a script is indeed one way to set a parameter. Another way, allthough with its limitations, is through the parameter page component.

The disadvantage of this approach is that

1. The parameter needs to be available on a page
2. You'll end up with th entire page, while you probably want to modify a single parameter.

There are (short term) plans however to have a dedicated component for this, available both in dashboards and Low Code Apps!

For now, you could create your own by combining a text/number feed with some buttons linked to a script. You could link the script to the feeds in order to dynamically change a selected parameter.

This workaround is only possible in Low Code Apps, as it relies on the button component. (Having this available in dashboards could be done with the Grid component)

Regarding the object manager instances

You are correct that the create and update capabilities are scoped to Low Code Apps only. This grew from the idea that dashboards are all about displaying data, while Low Code Apps is about doing something/anything with data.

Lately, we're stepping away from this initial idea and the edit capabilities will eventually also reach dashboards.