Is it possible to cancel an uplift project

So there are different methods of increasing relations with other empires:

• Establish an embassy: you can establish an embassy with the other empire in the same screen as the screen shot you provided. This will increase relations slowly until it reaches 100. You have a limit of 3 embassy by default but government type options can allow you extras.
• Rival the same empire: If the other empire has a rival, rivaling that empire will boost your relations by 25 ⁽¹⁾; this only lasts for the duration of the rivalry.
• Select xenophile traits: being a xenophile will increase other empire relations by 10, or by 20 if fanatic xenophile.

(1) Diplomacy - Stellaris Wiki: Opinion modifiers » Mutual rivals (17 May 2016)

No, it's just flavor text depending on your governments ethics. if you chose 3 ethics, you'll get 3 responses based on any combination of two. If you are fanatical, you'll get three options as well, one based on both of your ethic aspects, two based on one.

None however will influence the opinion of the other empire nor will they have any effect on future interactions.