There is no limit. The admin can create an unlimited number of RMA reasons in the modules –
- Magento Product Return RMA
- Magento Marketplace RMA System
- Magento 2 Product Return RMA
- Magento 2 RMA System Marketplace Add-on
The admin can edit the details of the existing RMA reasons. And the customers will be able to select and use these reasons for admin as well as for seller’s products while filing the RMA.