In "https://space.stackexchange.com/questions/1334/can-venus-be-made-habitable" we see that Venus's atmosphere would have to be substantially altered in order to terraform Venus.
"Why has Venus's atmosphere not been stripped away by solar wind?Why has Venus's atmosphere not been stripped away by solar wind?" tells us that even though Venus has no magnetic field, it does have an ionosphere generated by the interaction between solar wind and the thick atmosphere.
If we altered Venus's atmosphere substantially for terraforming, would it weaken this effect thereby destroying Venus's ionosphere?
In other words, if we made Venus have the same atmospheric thickness and composition as Earth, would its ionosphere be weaker than the Earth's?
If this is the case, then Venus's atmosphere would be at risk of being stripped by solar wind like Mars's was (see "https://space.stackexchange.com/questions/634/would-terraforming-mars-be-possible"). This would mean we would also need to create a magnetic field for Venus to truly terraform it.