Customizing “Tag It” field in Prologue theme

I’m using the Prologue theme and I want to replace the “tag it” field with 3 drop-down boxes. I want my readers to be able to pick three options each for tags for each post.

Another option I’ve considered it having a series of checkboxes, up to 10, where they can decide what applies to their post.

I’m doing this because I want to keep the input in the “tag it” field in a narrow range of options.

Any suggestions on how to do this?