f 4. If the answer to 3. is "yes", how long did the changes take?

From what I've read in the past, the required time is about 200 years, depending on how big a change you want to make. The big problem is that the changes seem just as likely to occur in your own society as in the society you're trying to change. basically you need to get past grandchildrens grandchildren to remove the memory of the initial invasion and memory of culture.

The only truely reliable way to chqange a society is for them to want to change themselves, and you can never guarantee that they will chose to change in the way that you want.

Any idiot can face a crisis - it's day to day living that wears you out.