If I've made some changes in the calculated variables formulas, is there any way to update them in the active application?

Yes, you can re-run calculations in applications however this does not automatically occur when the formula is updated (you must trigger the recalculation).
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To update a specific application through DigiFi's platform UI, please click on the application, then navigate to 3 dots button on the top in the right corner and choose "Re-Run Calculations".
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To update a specific application through DigiFi's API, use the "Run Application Calculations" endpoint found here.