I think this is a glaring omission from the X2Flow system. You're not able to retain data as a field to use after changing records in the flow.
My specific scenario is I want to be able to use dynamic lists to segment my database based on a custom field in a custom module. The simplest way to do this to what I can see is have a consistent dropdown between the custom module (where the value is set) and then a Flow to set it in a hidden field on the contact, so my dynamic lists can then adjust according to that criteria.
There's no simple way to do this.
I have to setup a workflow to remove contact from all the lists then go through all the options in the dropdown, really cumbersome.
Hopefully this should be an easy feature to add.