Can I customize my Nurture CRM integration?

Yes. You can customize your Nurture CRM integration.
You can define rules to select the contacts that should be pulled / pushed to your CRM account. These rules can be based on tags.
First go to Settings Tab by clicking on the gear icon located on the top right of your page. On the left pane, click on CRM Integration.
You will be directed to the detail page of your CRM Integration page.

There are some Custom Requirements defined, they are:
1. If you have additional custom requirements that you would like to configure then Please call to setup for your customized integration. And if you select this option, the rest three options will be disabled automatically.
2. You can push all the activity data for all contacts to Salesforce.com under Contact or Lead Activity History.
3. You can also push all contacts added in Nurture to Salesforce.com using Tags. When you select this option "Choose tags" dropdown will appeare. Here you need to define both Nurture defined tags and Salesforce Defined tags and click on "+" icon.
4. Lastly, you can update and over-ride Salesforce existing contact & account fields with Nurture contact & company fields respectively.
These requirements are placed with check-boxes in front of them. According to your requirements you can check-box the activities you need and leave the rest.