Upvote:2
In principle, you can make minor changes but you should not change your plans so drastically, especially if you have a single entry visa (which is likely as a first-time applicant). In practice, if you enter and leave through the same country, you are very unlikely to run into problems (although it's possible). See also this answer to another question.
But if you really intend to tour several countries from the get go, it's a bad idea to lie about it. You run the risk of contradicting yourself and damaging your credibility. And if you provide a plan for an 8-day trip, you are likely to get a visa valid for 8 days (or possibly 10 or 12 to give you a bit of leeway) and will not be able to stay for 30 days on it.