What changes does so for a simple reason: because it already is something. If it is beginning to be another thing or not, it does not matter in a existential standpoint.
Thus, by merely existing, the word already has its meaning, even if distorted, actualized, marginalized or adapted for newer times.
Also, we cannot confuse the words' meanings with the communicators' meanings. The person who emits some word can quite well mean something else than the widely accepted meaning of the word spoken/written, but, anyhow, even the perception of the change of significance is a sign that that word may not be in its most used fashion.
Words are the product of our creating as a species to understand each other and communicate our ideas. Each seperated geographical areas create their own version of verbal communication. Since we created the language we gave these words their meaning. So why wouldn't we be able to change their meaning.
Different languages, to me, show they have no intrinsic meaning. That, along with the fact that we can change the meaning of a world at our whim. We all just agree as to what they mean, that's what gives them meaning. Sometimes we don't agree and that makes a word meaningless.
Funny, I have to use words for my opinion! All joking aside, the very fact that there are so many languages, and in each one, there are varied and diverse meanings for the same word and many slang terms just goes to show that it is not possible to have intrinsic or inherent value in words. Even sign language has slang! The definition of these words, as we have come to agree on them of course, since they have no meaning, is a value that is FOUND, not given, whereas all words in all languages must be GIVEN value to be agreed upon, ruling out intrinsic value.