How to merge tags

Is it possible to merge tags a bit like you can do with the genre cleanup tool? I want to consolidate some tags and not sure how to go about it.

You can use a combination of Smartlists and Recipes.

For example, if you want to change the tag Bass to another existing tag called Bass Music then you can use the Replace Tag recipe. After that, you can throw away the Bass recipe.
That works for most situations to consolidate tags.

You can also create a smartlist to find tracks with multiple tags or any combination of tags. Then use the Add Tags or Remove Tags recipe on those.