no I believe you do not need to change the revision number each time you make a change.
The revision number in combination with the MST name is used as a unique way to identify a MST Region.
This is what the IEEE 802.1s doc says about the Configuration Identifier ( NAME + Revision Number)
--Section 13.7
It is essential that all Bridges within an
MST Region agree on the allocation of VIDs
to specific spanning trees. If the allocation
differs, frames for some VIDs may be duplicated or
not delivered to some LANs at all. MST Bridges
check that they are allocating VIDs to the same
spanning trees as their neighboring MST Bridges
in the same Region by transmitting and
receiving MST Configuration Identifiers
along with the spanning tree information.
These MST Configuration Identifiers, while
compact, are designed so that two matching
identifiers have a very high probability of
denoting the same configuration even in the
absence of any supporting management practice
for identifier allocation.
--
