We are thinking of upgrading our current motor to make more power. The upgrade will require 91 octane fuel to be used to prevent predetination. We only have access to 89 at our local lake. Can we use octane booster with 89 octane fuel on a regular basis?

yes

Yes, but it wont help. When they talk about 2 points or 4 points, they are .2 or .4. They are plenty of threads about this subject. You need a ton of it to do any good and then its still dangerous. Many people keep a bunch on board in case they get stuck and have to use marina fuel but Id never depend on it full time. Better to build the engine to run on 89 or fill it yourself.

my experience w/ all manner of these products in the car industry is that they are essentially worthless... not to mention how much you would have to pour in to allegedly convert your 100 plus gallons of gas to what you would like to believe is good fuel. my opinion is that you are asking for potentially very expensive trouble.

either build the motor with a compression ratio that will run on what you have avaialble or be prepared to supply your own .