prefix (something) to (something else)
To attach a particular prefix to the beginning of a word. Confusingly, prefixing "in-" to "flammable" doesn't create a negative, which is what you would normally expect. You need to prefix something to it if you want to change it from a noun to a verb.
prefix something to something
to place something at the beginning of a word or part of a word. If you prefix a re- to some verbs, you get an entirely different meaning. You can't prefix anything to some verbs.