Can I change my settings after I have logged shifts?

Yes. Change anything you like - your fuel price, your MPG, your insurance, your mileage rates - and nothing you have already logged moves.

When you log a shift, JoltMile saves the settings in force at that moment onto that shift. Every figure the shift ever produces is worked out from its own saved copy. That is what makes last March comparable with this March: if a price rise reached backwards, every figure you had already looked at would change under you.

It holds even when you edit an old shift. Opening a six-month-old shift to correct its notes does not re-price its fuel at today's pump price.

If one shift genuinely was priced wrong - you filled up cheaper that week - edit it and change the price on the review step. That re-costs that one shift and nothing else. There is one deliberate exception to all of this: changing an insurance rate asks whether you want it applied to past shifts, and does it only if you say yes.