Hi Uday,
This is Spencer 
. You may remember me.
There is no attribute for BP relationship. You will need to firstly define the attribute in Maintain Territory Attributes and code your logic in BADI: Implement Business Logic for Additional Attributes.
You may read the document first.
You may refer document Customer Relationship Management (SAP CRM)
Personally, I have never seen any customer who requires establishing account - territory relationship based on BP relationship. Who will be the source of the BP relationship? How to assign it to territory? I do not an answer. You may have to implement the logic in the badi.
At the end, the final result of maintaining account - territory relationship is to update the crmd_terr_accrel table which is the relationship table for account and territory. This table is used during territory determination and territory check (note 2291621 ) rather than calculate the rules (performance). Consequently, you have to consider updating this table. There are 2 ways.
1, run report CRM_TERRMAN_BUILD_REL during non business hours, or
2, dynamic update of relationship
Spencer