... what allowed the Federation not to remove the colonists in Journey's End wasn't their renouncing their citizenship, it was the Cardassians permitting them to stay ...
By choosing to renounce their citizenship, they are no longer Starfleet's responsibility, & therefore they would not be able to remove them forcibly.
As I recall, Picard was ordered to remove the colonists, not to remove "Federation citizens." Regardless of their citizenship status, if the Cardassian hadn't agreed to allow them to stay, Picard ultimately would have removed them. This was a condition to the new treaty. Whether they were leaving (or not) wasn't really up to the colonists.
Starfleet was evacuating non-Cardassians
from a Cardassian