Yes You can. But please note that CAN1 and CAN 2 bus speed change must be done only when vehicle's Ignition is OFF.
Once vehicle is off send these commands:
for CAN1 bus speed " setparam 205:<bus speed>"
for CAN2 bus speed " setparam 207:<bus speed>"
Possible bus speed values: 50, 100, 125, 250, 500 and 1000
Please note there are 2 blank spaces before the command if You have not set login and password for SMS sending.
If You do, SMS commands should look like this:
for CAN1 bus speed <login> <password> setparam 205:<bus speed>
for CAN2 bus speed <login> <password> setparam 207:<bus speed>