On my project, it quite rapidly increases a variable (http://scratch.mit.edu/cloudmonitor/11301700/). Could there be an option, if it does this, to only have the cumulative change on exiting the project?

Maybe you could make a variable (not in the cloud) that keeps track of the variable and how much you increase it, then have some button that says something like ‘press this when you are done’ and it adds that variable to the cloud variable. The only problem is that people may not press the button, therefore not giving an accurate account of the cloud variable.