Can I get a re-entry permit for my 90-day Non-B visa to make a second entry before it expires?

Yes, if you have a 90-day Non-B visa (single entry) and you want to travel outside Thailand during your visa validity, you can obtain a single-use reentry permit either at an immigration office or at the airport before you leave. This will allow you to return to Thailand without invalidating your visa. Just remember that the visa will be considered used after the first entry, but the reentry permit allows your stay to continue until the original expiry date.