While on-the-fly deposits and withdrawals are possible and mostly oriented towards end-users, there is a way to perform conversion of funds (either crypto to fiat, fiat to crypto, or crypto-crypto) with existing merchant balances as long as the exchange pair is supported by the processing. The exchange feature is available via API
The minimum exchange amount is equivalent to 0.003 BTC (This limit does not relate to the on-the-fly deposits and withdrawals. In order to get the actual information about the on-the-fly transactions please refer to the Confirmations and Limits section).
More detailed information about min limits of exchange operations for particular currencies must be obtained via API (see this API call) because they may vary dynamically.