Hi,
Short answer - yes, expo can be changed in G3.5.
However I have no idea if the model you are flying on your sim has expo set or not.

Go into the 'aircraft' then select 'edit XXXXX' (where XXXXX is the model you want to use)
When the edit screen opens go to Software Radio and select Output Channel.
Here you will see and be able to change the expo values for both low and high rates.
They are shown as channel 1,2,3...
To see which ch number controls what go to Radio Display, also under Software Radio.

Hope this helps.