I got intrigued by this question and the suggestion in another topic to use jquery to manipulate the variables, got stuck, didn't want to give up, got it sort of working, but not sure if this really is the best way to do it.
You can download an example that I created. It asks for your name and uses 3 variables: health, stamina, experience.
On each page you get a number of options. You have to select an option first, then hit submit.
The form checks if a value in a variable has changed, so I have a set of input fields in a hidden div (hidden by the css of the page).
Depending on the selection that you make, the input fields get updated with the new values the variables should get (based on the current displayed values).
I tried to combine submit of the form and selection, but that didn't work because the event handler for the submit button always fires first before I can change the value of the input fields.
The css doesn't need to be there for every page, just add it to a stylesheet that you attach to the LO.
The script needs to be set for every page and you need to be comfortable working in the source view.
I don't seem to be able to disable the pop-up message and there is nothing to prevent a user from skipping a step.
Would this be something that could be better realized using a decision tree? Would I still be able to tally choises?