Congratulations on using the manual. Not everybody does that.
Sounds like a good plan. It should work to cover the advice found in your manual and save some money.
I grew up with the old Sunoco brand gas stations that let customers blend their octane at the pump. Underground were 2 tanks (high octane & low octane) and the customer would move a dial and select octane ratings from a range of choices. Of course the gasoline was priced accordingly, higher octanes costing more than lower.
CSA