Be able to update a token value from a flow step

This idea is to create a "change token value" flow step that would enable to dynamically update the value of a token from within a smart campaign. There would be 2 options:

1. The change would be only visible from within the campaign flow, similarly to what can be done with the "request campaign" API. Therefore, all emails sent from within this campaign will use the changed value for the lead. The main use case of this would be to reduce the number of emails. The same email could be sent 2 or 3 times at different points in time from the same campaign with different content or subject.
2. The change would be impacted at program level and it should be possible to either set the value or add values to a token (similarly to a score). The main use case would be to enable to count the number of attendees in a program.

-Greg