It is very important you are careful when making changes to the question set once live data has been recorded. Changing question or answer option orders (only through use of the Up/Down facility) is fine as is changing question text/headers etc… But any change to the substance of the question (the type or the answer options) will impact on the data integrity of your results.

If you add a question or option only those answering after the addition can answer but statistics are based upon the whole set of respondents for example. Deleting questions or options may also have unforeseen effects.

If you really need to make changes I suggest you either…

(a) copy the set structure into a new question set, publish that and take the original off-line then amalgamate the results accordingly or;
(b) take a data snapshot (see 3.3.3) and use it to adjust/reduce the later full results set.