Kusto user-defined function for common actions

I'm looking to leverage common functions across a number of queries so we can update in one place rather than in every analytic.

First question, would it be possible to have a function that just defines a dynamic variable that can be used in other analytics. E.g. a function that defines a list and saved as lb_primaries.

let lb_primaries = dynamic(["127.0.0.1", "127.0.0.2", "127.0.0.3"]);

This way we could reference lb_primaries in a number of analytics, but only update in a single place?

The second question, using an example of a basic lookup (I'm aware of externaldata) where we can return a true or false based on the input. E.g. is_primary_fn

let is_primary = (ip:string) {
    iif(dynamic([
        "127.0.0.1",
        "127.0.0.2",
        "127.0.0.3"
    ]) contains ip, true, false)
};

Then using that with a query like:

NetworkData
| where is_primary_fn(IPAddress)

Which in this example fails with "Body of the callable expression cannot be empty". I've tried a few different way to get this working but so far not having any luck 😞