Well, it is possible if you provide which all currencies need to be displayed in the announcement bar beforehand.
It involves adding code to make the setting for showing the appropriate message on the announcement bar based on the currency selection.
Please let me know if you would like to discuss it further.
Nick here from Shopify. Great question!
Can I ask how you currently have your announcement bar? For example, is it through the theme natively or do you have it via an app? I think this is something that could be accomplished much easier via an app. If it was through the theme natively, it could require some custom code changes if it's not enabled already.
I did, however, find an app where this is an available feature. It's the Free Shipping Bar by Hextom app which you can find here. You can see from the screenshot below where the app developers mention this in the app description:
All the best, Nick
I wouldn't be very proficient in code personally, and would not be comfortable offering advice on this because of that. My advice would be to reach out to the app developer directly about this. They would know best about any code for their app and about merging it with another app such as the Free Shipping Bar. You mentioned it was the Multi-Currency Converter app and you can see their website and support section here.