Can I stop selling to one country for a while without removing it?

Yes. Go to Settings → Store Settings → Selling Location and click Edit on the country. Change Status from Enabled to Paused and click Update.

While it's paused, the country is left out of the country list on your storefront address forms, so new customers there can't choose it. The list on the page shows Paused next to it.

When you're ready, edit it again and set Status back to Enabled. Use Delete only to remove the country completely.

If you pause every country, the address forms show the full country list instead.