You can definitely switch hotels or make some small changes to your itinerary. This should not invalidate your visa (but see Andrey's answer regarding some questionable practice by some Schengen countries). Going to a different country could be slightly more risky but it's still generally possible. For example, stopping somewhere on the way, changing the order of countries or adding a new destination to a trip is perfectly OK. By contrast, using a visa for a completely different purpose is not (at least in theory).
Specifically, the rules are laid out in article 34 of the Schengen Visa Code:
A visa shall be annulled where it becomes evident that the conditions for issuing it were not met at the time when it was issued, in particular if there are serious grounds for believing that the visa was fraudulently obtained. A visa shall in principle be annulled by the competent authorities of the Member State which issued it. A visa may be annulled by the competent authorities of another Member State, in which case the authorities of the Member State that issued the visa shall be informed of such annulment.
A visa shall be revoked where it becomes evident that the conditions for issuing it are no longer met. A visa shall in principle be revoked by the competent authorities of the Member State which issued it. A visa may be revoked by the competent authorities of another Member State, in which case the authorities of the Member State that issued the visa shall be informed of such revocation.
Annulment is more serious than a mere revocation because it's a black mark on your record. It implies that you lied to obtain a visa.
In practice, if you show up somewhere unexpected, say in Germany with a visa for Greece, you might get a few questions about that. If you have a good explanation and all the necessary documents, there is no reason you would be denied entry and/or your visa revoked but if the border guards think you lied to get a visa and you always intended to come to Germany, they can annul it and send you back.
So the answer is not a clear-cut “your visa will become invalid if you change your hotel” but it's not “this visa is valid for anything anywhere within the Schengen area” either. Border guards have to decide whether it looks like you obtained your visa fraudulently and they do have the power to invalidate it if they think that's the case.
In your case, you are still going to typical tourist destinations, you would be entering through the same country as originally planned and the itinerary sounds very similar to the one you submitted when applying to the visa so I would not expect any problem. In all likelihood, the border guards in Prague won't even ask you anything beyond routine questions. If you are leaving in time, the border guards in France obviously have no reason to be concerned either.