We don't currently have any import functionality that uses files to update tax schedules. It's also not currently on the road map. However, we do realize how frustrating the act of updating taxes can be. In some jurisdictions, taxes can change as often as several times in a single month. Also, taxes in many jurisdictions have overlapping zones. For example, one of our co-founders has a different tax zone than some of his neighbors, despite living in the same zip code. This is much more common than you might think.
For those reasons, we added the native integration for Avalara's Avatax product. This product is a cloud-based subscription service that does all of the tax updates for you. No need to update your tax schedule any longer.
If you can't use this service, you can still achieve that you're looking for, but since it's not an out-of-the-box feature, it would need to be built as a custom module or scheduled job. In either case, the code should be pretty straightforward since there's numerous examples out there for how to read an Excel spreadsheet, and you'd be able to manage taxes using our REST API.
If you don't have the time or resources to do this, we can match you up with one of our expert e-commerce partners.
Finally, if you really think this should be an out of the box feature, you also let us know by submitting a comment below, and/or by submitting a support request. Another way to make this happen is through sponsoring an enhancement.