Double layer skylight in Carriage Cameo question?

I am in the process of re-caulking and sealing everything on my roof, and decided to replace the skylight dome over the shower on my Carriage Cameo.

I have now found out that there is an inner and outer dome on the Carriage, but that the inner dome is not part of the inner trim ring as I thought it was.

Can someone tell me if I can just replace the outer dome and how all this fits together....I have not yet broken the seal on the roof and would like to know if I can do what I want to do....

Thanks!