Source: Paizo Inc. - Inner Sea Primer, p.17
Selecting a Region of Origin permanently disallows using Regional Traits associated with other Regions of Origin.
For example, if I select Qadira as my Region of Origin, deselecting it and choosing Steaming Sea as my Region of Origin disallows taking the Hermean Paragon Regional Trait.
1. Take Qadira origin.
2. Take Genie-Caller trait.
3. Remove Genie-Caller trait.
4. Remove Qadira origin.
5. Take Steaming Sea origin.
6. Taking Hermean Paragon is disallowed.
@Code PREREGION not updating like other PRExxx tags.
I guess a workaround is change Regions to Facts, and move away from using PREREGION.