The concept of modern Italy is a result of three main factors:
1. Versailles order of Europe after Napoleonic wars
2. Territorial Claims of Sardinia and Piedmont
3. Spring of Nations movement in Europe and rise of nationalist ideas that gave ideological fuel to this process.
Italy as a modern country we know began in 1859.
As for Renaissance Italy, it was never a united geographic area. It was never ruled by one center of power in contrast to Medieval Germany HRE.
In Rennesaince Era Italy we had various different lands with similar cultures and langue but they would never call themselves Italians. It all makes a Ressaince Era Italy a perfect example of a blob Civ.
To complicate things more if we are talking about modern Italy as a Civ Rome is a perfect capital (Capital of Kingdom of Italy since 1871)
As it comes to my personal opinion I was always against this strict "blob Civ" approach and I never had a problem with The Celts as a Civ (when we are talking about continental ones, things with British Celts are more complicated). So Renessaince Italy would be ok for me. Even with Rome as capital. But some of us who are more strict with the idea of de blobing Civs might have a hard nut to crack