The number of treatments in the design is currently 16 in 2 blocks and we will increase and revise this during the pre-test, pilot and main survey. How do we handle this?
This is fine. Even if the design changes, the DCE data has the levels allocated included.
What you should watch out for however is if the DCE structure changes.e.g. different number of alternatives, attributes, levels or the 'labels of the levels. This will make merging the experiment problematic as data won’t have the same meaning.