Just share my experience about request replacing Master with Visa for Maybank 2 card. I went to KLCC to make above request and the process be told as below:
1) they will send the new card request to process (2 hrs done if request made during weekdays working hours)
2) after the new card (Visa) is received, you need to ask staff to help you cancel the existing card (Master) and transfer all TP and outstanding (if any) to the new cards from existing card upon you collect in KLCC
3) you will receive RM50 charge shown in the following month statement
4) you can come to KLCC and opt to request waive the above charge but subject to management discretion