Hello & Welcome to the Forum!

I do not think that it would be easy to exchange the O-31 to 0-36 piece of track in the switch, but won't say it is impossible.  When l install a switch, regardless of curve diameter, l insert a straight then make my transition into the curve. That helps keep you from derailing as you come out of the switch, and you can go into any size curve you wish. 

Hope this helps...
Happy Rails.
dave