Your plan to do one month of Muay Thai for a 5-year visa will likely cause issues at some point. The purpose of a Muay Thai DTV is to actively train in Muay Thai.

1. Many embassies refuse applications for only one month.

2. Extensions in Thailand require proof of ongoing training.

3. Border officials may ask questions when crossing.

4. Document checks at the border are possible but not common (I've heard of at least one case).