Joshua
So in other words (just making sure I'm understanding what you're saying) you can switch from a dry tire to a rain one, but can't switch from a rain tire to a dry one?
In answer to your question...
Yes you can switch from a rain tyre to a dry one providing you have selected the dry one in your main strategy stint 1.
The tyres available on the grid for a wet race are your main strategy stint 1, Inters and Full Wets. So if you have selected either of the wet type compounds for stint 1 in the main strategy you
will not have a dry compound tyre available to you on the grid. If however you selected a dry compound for stint 1 then you can select from both wet type tyres and the dry stint 1 compound... If that makes sense LOL.