1) Changing words
You'll need to use buttons with no background so only the text shows and use ifelse tests to determine what the text should change to.
2) Copy/paste in blocks editor
You can select the block and use ctrl+c / ctrl+v. You can't do that from one app to another, but that's on the feature list.
3) Multiple pages
Please see my tutorial Creating Multiple Pages
Creating Multiple Pages - App Inventor Info Center
4) Clock as calendar
Check out the clock tutorial's on Ed's site Blocks123
. You could probably use something there to accomplish what you need.
App Inventor Info Center