Don't worry too much about that, it's just standard blurb that all holiday companies use in their T&C's to cover themselves for any eventualities, it's rare for advertised hotels to be changed at the last moment.
but, if they did change and the new hotel is not up to scratch, don't be English and suffer in slience! complain to the tour manager/rep, if they don't resolve your complaint get straight onto Head Office, don't wait until you've come home!
Also, social media is a powerful tool nowadays, if you post your experiences online, twitter, facebook etc and they are not good, you'll be amazed at quickly problems can suddenly be resolved!
Knowing and experiencing how good Just You are at resolving problems, I'm confident this advice will appear!
Enjoy your holiday, thats the main thing to think about!