As it's mentioned in the Intel Edison Compute Module Hardware Guide ( http://www.intel.com/support/edison/sb/CS-035274.htm), in order to modify the internal pullup values and current assist setting the MIP Header of the firmware must be modified. This is not advice as it could potentially make the I2C bus behave unexpectedly.
I hope this information helps.
For the pull-up resistor you edit the file /sys/kernel/debug/gpio_debug/gpioXX/current_pullstrength. My question is what file do you edit to modify the current assist or has that even been implemented? Also, per table 13 of the Intel Edison Module Hardware Guide it is advised to use the current assist.
I've been investigating about this and unfortunately I found out that it is currently not possible to change the current assist settings. This might change in future releases, however, there's no ETA for when an update will address this feature.
I apologize for any inconvenience this might cause.