Is there any way to target the loss of slow twitch muscle fibres without effecting my performance?
I'm not sure what you think you can target or avoid. I do know that if you are new to cycling, and new to aerobic exercise (endurance) then you probably would want to continue to develop more slow twitch fiber capacity.
The simple answer to your situation is to continue to exercise in the sports you want to be good at and avoid exercising muscles you don't use in that sport. If you are so dedicated to a sport that you are exercising at low fat-storage levels - it is unlikely you will be building much additional muscle mass, anywhere.