You could actually turn them into urban center, buy buildings and revert back to growth.
The only problem for Carthage is that you can't make them Trading posts, but with libraries it's not that big deal.
I have done that with Towns that I wanted to pick up a few more resources, but weren't growing very fast.
Desired civs for Civ 7: Hittites, Minoans, Franks, North Sea Empire, Iceland, Ireland, Iceni, Picts, Bohemia, Romania, Kyivan Rus, Muscovy, Madagascar, Ethiopia, Berbers, Almohad Caliphate, Seljuks, Burma, Vietnam, Tlingit, Navajo, Commanche, Cherokee, Haudenosaunee, Taino, Haiti, Argentina
Desired leaders for Civ 7: William the Conqueror, Alfred the Great, Aethelflaed, Canute, Boudicca, Julia Domna, Brian Boru, Grainne O'Malley, Carl Gustaf Mannerheim, Karl Marx, Ivan the Terrible, Rasputin, Timur, Shah Jahan II, Ranavalona I, Dihya, Yusuf ibn Tashfin, Abd el-Krim, Sequoia, Anacaona, Hoskannini, Tupac Amaru II, Toussaint L'Ouverture, William Wilburforce, Garibaldi, WEB duBois, Mary Wollstonecraft, Alfred Nobel, Simon Bolivar, Lili'uokalani, Roxalana, Hassan-i Sabbah