Allied Telesis AT-S62 - Manual (Page 422)

Chapter 27: MSTP Commands
422
The PRIORITY parameter specifies the new MSTI priority value. The range
is 0 (zero) to 61,440 in increments of 4,096, with 0 being the highest
priority.
Examples
This command changes the MSTI priority value to 45,056 (increment 11)
for the MSTI ID 4:
set mstp msti mstiid=4 priority=11
This command changes the MSTI priority value to 8,192 (increment 2) for
the MSTI ID 6:
set mstp msti mstiid=6 priority=2