Currently the SFDC campaign token only can be used as a value in Add in SFDC Campaign or Change Status in SFDC Campaign flow steps. It can NOT be used in a choice of a flow step, so it's impossible to change status of existing members of a SFDC campaign using the token.
It would be great if I was able to do something like that
Change status in SFDC Campaign
Choice 1: If member of SFDC campaign {{my.SFDC campaign}}
Status in {{my.SFDC campaign}} = Registered
Default: Do Nothing