They would have to take apart the car to do that dependent on what specific changes you wanted made. In the game while you are in the race the only adjustments you can make are wing adjustments. If anything if it is a race where there is a possible chance of rain and clear weather than you should set your car up for the dry weather and suffer with the car with the wet tires on.
The only adjustment that is doable mid race are wing adjustments. What you could do is work on a setup to adjust the car off your dry setup with just wing adjustments.
Meaning if you have a dry setup you like then practice with wet conditions but only make changes to the wings and nothing else. This way you know what to change and have been accustomed to racing in those conditions with those wing adjustments.