Snipe-IT offers a way to bulk regenerate asset tags all at once, but updating only certain asset tags in bulk can only be done via API, since asset tag is currently the unique identifier for assets within Snipe-IT.
This Google App Script will let you provide a list of Asset IDs and the new asset tags they should use, along with showing you the status of the request, without having to know how to write code to use the Snipe-IT API.
This script expects a CSV that has a header row (though it doesn't matter what the header names are) with the first column being the internal Snipe-IT asset ID, and the second column being the new asset tag you want to change it to.