Hi @AzzaB.
It is possible today to return variables from a Composer dialog, which you can then use within PVA, to do things like call a Flow, for example.
To do this, you need to set the input / output properties on your Composer dialog. In the screenshot below, I have added two output properties (Variable1 and Variable2, both strings).

Once you have configured your output variables, you can assign values to them within Composer. They sit within the dialog result, so to assign a value to Variable1, you would set your value into dialog.result.Variable1 (an example of this is shown below).

Finally, once you publish your Composer dialog back to PVA and add a redirect to it to your canvas, you will see the output variables are now shown and are available to use within PVA.

Right now, you are limited to multiple primitive properties, as opposed to returning objects, which means you might need to do some variable manipulation within Composer.
Does this help with what you are looking to achieve?