Yes, this is possible. Based on your requirement, you can set the custom field status in the customer portal & checkout pages.

If you're using the V2 checkout pages & V1 portal, this option is available under Settings >> Checkout & Self-Serve Portal (under Customer-facing essentials section) >> Field Configurations (on the left panel) >> Custom Fields for Customer/Subscription. Here's a screenshot.

Similarly, if you are using the V3 checkout pages and V2 portal, navigate to Settings >> Checkout & Self-Serve Portal (under Customer-facing essentials section) >> Fields. 

You will find the customer level custom fields under Account Information and the subscription level custom fields under Custom fields for subscription tabs respectively on the left panel. Just pick the appropriate custom field, enable it and click the edit icon to set the status. When you're done making changes, just Publish it.  Screenshot is below.