Adding to this thread with info some may find useful:
I can report that it is 100% possible to have a Thai spouse added as a beneficiary to your existing April International (France) policy—even if they are living in Thailand full time. I have now successfully done this with my wife after we returned to Thailand from our previous residence abroad. Previously my wife had a separate April International policy while she was herself an expat in the EU, but I don't believe this matters. They only seemed to care that we were married. Some other things to know:
Unless your spouse is already insured with April International at an equal or superior level of benefits to you, they will need to submit a new health questionnaire and go through underwriting just as if they were applying for a new policy.
Both you and your spouse will be insured on the same policy, so your specific plans will also be the same (you can't insure one of you at a higher/lower level of benefits).
It appears that as long as your marriage is valid in France, it's valid for this purpose. This is important for same sex couples whose marriages are not considered legal in Thailand. We have only a US marriage certificate. We were not asked to have this translated or certified in France or the EU.
We only needed to provide the following documents for my wife:
Passport
A special 1-page form (similar to an application form)
Health questionnaire + any relevant medical records
April states that your spouse will be added to your policy "on the 29th of the month following medical acceptance." In our case it was completed immediately after medical acceptance, about a week after we submitted the documents.
Once your spouse is added, you'll receive an invoice for a pro-rated premium—to catch your spouse up to your existing policy term. You'll then renew together as a single policy.