The go-exif project is now available. It allows you to parse and enumerate/visit/search/dump the existing IFDs/tags in an Exif blob, instantiate a builder to create and construct a new Exif blob, and create a builder from existing IFDs/tags (so you can add/remove starting from what you have). There are also utility functions to make the GPS data manageable.
I have also published go-jpeg-image-structure and go-png-image-structure to actually implement reading/writing Exif in those corresponding formats. PNG adopted Exif support in 2017 and this project was primarily meant to provide PNG with fully-featured Exif-writer support both via library and via command-line tool.
go-exif includes a command-line utility to generally find and parse Exif data in any blob of data. This works for TIFF right off the bat (TIFF is the underlying format of Exif), which I did not specifically write a wrapper implementation for.