All you are changing is what is modified and what is modifying.
While 友達は親切じゃない人 is grammatically acceptable, it is not a complete sentence as it stands. You have marked 友達 as the topic, have said the noun 親切じゃない人, but have not included a verb. One could say 友達は親切じゃない人なんです (or some other variation on the state-of-being) to close the phrase, although this is probably more roundabout than one needs to be. 友達は親切な人じゃない is a complete sentence as is.
For the second, you are again only reversing what is modifying what. The second, 高い値段レストラン, would probably be 高い値段のレストラン in more proper speech. Particles like の tend to disappear without a reason in casual speech though, so it not being there isn't so big of a deal.
All you are changing is what
All you are changing is what is modified and what is modifying.
While 友達は親切じゃない人 is grammatically acceptable, it is not a complete sentence as it stands. You have marked 友達 as the topic, have said the noun 親切じゃない人, but have not included a verb. One could say 友達は親切じゃない人なんです (or some other variation on the state-of-being) to close the phrase, although this is probably more roundabout than one needs to be. 友達は親切な人じゃない is a complete sentence as is.
For the second, you are again only reversing what is modifying what. The second, 高い値段レストラン, would probably be 高い値段のレストラン in more proper speech. Particles like の tend to disappear without a reason in casual speech though, so it not being there isn't so big of a deal.
Hope that was sensical enough for you ^_^"