Declaring them hostile won't change their opinion of you, unless you open fire. If they have already begun sharing geological survey data with you, then they are likely to have already declared you to be a friendly empire. Prior to this you could have parked a warship in their space to impose a penalty to their opinion of you, but once you are considered friendly, that penalty is waived.
If you have declared them friendly or allied, you can reduce this to neutral (or hostile). If you have any treaties with them, including trade access, you can revoke those treaties. At that point, if their diplomacy team assigned to your empire can't overcome their racial xenophobia score, their opinion of you will begin to decrease, eventually to the point where they no longer have the option to share data with you.
It's more complicated than bombing their homeworld, but also less drastic.
