Is it possible to edit the Territory picklist on the My Accounts view page Online?
No, it is not possible to edit the picklist values. The Territory picklist contains the Territories to which the user is assigned. It includes all of the Territories that directly roll up to the selected Territory in the Territory Hierarchy.
The Accounts displayed in the My Accounts page are based on the value selected from the picklist. It shows all accounts assigned to that territory, as well as the Accounts assigned to its child Territories.
CRM Help Documentation: My Accounts