Hello Jae-Hoon Choi,
There is no problem to change the protocol per HCA.
For that, you can install Mellanox firmware tool (MFT) from Mellanox public website and use the mlxconfig tool.
For example:
mlxconfig -d <MST device> set LINK_TYPE_P1=2 LINK_TYPE_P2=2
Additional information can be found in the MFT user manual.
Viki.