Adjusting an existing discursive piece to change it to an imaginative one on the spot can be challenging, especially if there has not been enough prior practice and preparation. This is the reason that substantial practice is important to effectively prepare for such a possibility. You should therefore attempt numerous Module C questions that require a discursive response, and then practise modifying your responses to become appropriate for questions requiring an imaginative response. The more you do this, the better your ability to think on the spot/under pressure and quickly identify ways through which you can make adjustments.
In terms of specific adjustments that would need to be made, the main features of an imaginative piece (such as the ones that you mentioned) will need to be incorporated as an essential and prominent aspect of your piece. This could also mean the removal of features associated with discursive writing (thereby avoiding ambiguity caused by inconsistent writing), although it may not necessarily be the case. With some adjustments, the discursive piece can be contained within an imaginative piece. For example, a speech can be included as a significant event occurring within an imaginative piece. It can be delivered by a character and can address a certain audience within the imaginative.
I hope this helps!
